diff --git a/reana_commons/openapi_specifications/reana_server.json b/reana_commons/openapi_specifications/reana_server.json
index 4db3989b..4a32e68f 100644
--- a/reana_commons/openapi_specifications/reana_server.json
+++ b/reana_commons/openapi_specifications/reana_server.json
@@ -2,7 +2,7 @@
   "info": {
     "description": "Submit workflows to be run on REANA Cloud",
     "title": "REANA Server",
-    "version": "0.9.1a3"
+    "version": "0.9.1"
   },
   "paths": {
     "/account/settings/linkedaccounts/": {},
@@ -3955,6 +3955,189 @@
         "summary": "Set status of a workflow."
       }
     },
+    "/api/workflows/{workflow_id_or_name}/unshare": {
+      "post": {
+        "description": "This resource unshares a workflow with another user. This resource is expecting a workflow UUID and some parameters.",
+        "operationId": "unshare_workflow",
+        "parameters": [
+          {
+            "description": "The API access_token of workflow owner.",
+            "in": "query",
+            "name": "access_token",
+            "required": false,
+            "type": "string"
+          },
+          {
+            "description": "Required. Workflow UUID or name.",
+            "in": "path",
+            "name": "workflow_id_or_name",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "description": "Required. User to unshare the workflow with.",
+            "in": "query",
+            "name": "user_email_to_unshare_with",
+            "required": true,
+            "type": "string"
+          }
+        ],
+        "produces": [
+          "application/json"
+        ],
+        "responses": {
+          "200": {
+            "description": "Request succeeded. The workflow has been unshared with the user.",
+            "examples": {
+              "application/json": {
+                "message": "The workflow has been unshared with the user.",
+                "workflow_id": "cdcf48b1-c2f3-4693-8230-b066e088c6ac",
+                "workflow_name": "mytest.1"
+              }
+            },
+            "schema": {
+              "properties": {
+                "message": {
+                  "type": "string"
+                },
+                "workflow_id": {
+                  "type": "string"
+                },
+                "workflow_name": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "400": {
+            "description": "Request failed. The incoming data specification seems malformed.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Missing data for required field."
+                ],
+                "message": "Malformed request."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "403": {
+            "description": "Request failed. User is not allowed to unshare the workflow.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "User is not allowed to unshare the workflow."
+                ]
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "404": {
+            "description": "Request failed. Workflow does not exist or user does not exist.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Workflow cdcf48b1-c2f3-4693-8230-b066e088c6ac does not exist"
+                ],
+                "message": "Workflow cdcf48b1-c2f3-4693-8230-b066e088c6ac does not exist"
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "409": {
+            "description": "Request failed. The workflow is not shared with the user.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "The workflow is not shared with the user."
+                ],
+                "message": "The workflow is not shared with the user."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "500": {
+            "description": "Request failed. Internal controller error.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Internal controller error."
+                ],
+                "message": "Internal controller error."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          }
+        },
+        "summary": "Unshare a workflow with another user."
+      }
+    },
     "/api/workflows/{workflow_id_or_name}/workspace": {
       "get": {
         "description": "This resource retrieves the file list of a workspace, given its workflow UUID.",
diff --git a/reana_commons/openapi_specifications/reana_workflow_controller.json b/reana_commons/openapi_specifications/reana_workflow_controller.json
index ba596536..f66dce6b 100644
--- a/reana_commons/openapi_specifications/reana_workflow_controller.json
+++ b/reana_commons/openapi_specifications/reana_workflow_controller.json
@@ -2,7 +2,7 @@
   "info": {
     "description": "Submit and manage workflows",
     "title": "REANA Workflow Controller",
-    "version": "0.9.1a2"
+    "version": "0.9.1"
   },
   "paths": {
     "/api/workflows": {
@@ -1418,6 +1418,183 @@
         "summary": "Set workflow status."
       }
     },
+    "/api/workflows/{workflow_id_or_name}/unshare": {
+      "post": {
+        "description": "This resource allows to unshare a workflow with other users.",
+        "operationId": "unshare_workflow",
+        "parameters": [
+          {
+            "description": "Required. UUID of workflow owner.",
+            "in": "query",
+            "name": "user_id",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "description": "Required. Analysis UUID or name.",
+            "in": "path",
+            "name": "workflow_id_or_name",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "description": "Required. User to unshare the workflow with.",
+            "in": "query",
+            "name": "user_email_to_unshare_with",
+            "required": true,
+            "type": "string"
+          }
+        ],
+        "produces": [
+          "application/json"
+        ],
+        "responses": {
+          "200": {
+            "description": "Request succeeded. The workflow has been unshared with the user.",
+            "examples": {
+              "application/json": {
+                "message": "The workflow has been unsahred with the user.",
+                "workflow_id": "cdcf48b1-c2f3-4693-8230-b066e088c6ac",
+                "workflow_name": "mytest.1"
+              }
+            },
+            "schema": {
+              "properties": {
+                "message": {
+                  "type": "string"
+                },
+                "workflow_id": {
+                  "type": "string"
+                },
+                "workflow_name": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "400": {
+            "description": "Request failed. The incoming data specification seems malformed.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Missing data for required field."
+                ],
+                "message": "Malformed request."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "403": {
+            "description": "Request failed. User is not allowed to unshare the workflow.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "User is not allowed to unshare the workflow."
+                ]
+              }
+            },
+            "schema": {
+              "properties": {
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "404": {
+            "description": "Request failed. Workflow does not exist or user does not exist.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Workflow cdcf48b1-c2f3-4693-8230-b066e088c6ac does not exist"
+                ],
+                "message": "Workflow cdcf48b1-c2f3-4693-8230-b066e088c6ac does not exist"
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "409": {
+            "description": "Request failed. The workflow is not shared with the user.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "The workflow is not shared with the user."
+                ],
+                "message": "The workflow is not shared with the user."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          },
+          "500": {
+            "description": "Request failed. Internal controller error.",
+            "examples": {
+              "application/json": {
+                "errors": [
+                  "Internal controller error."
+                ],
+                "message": "Internal controller error."
+              }
+            },
+            "schema": {
+              "properties": {
+                "errors": {
+                  "items": {
+                    "type": "string"
+                  },
+                  "type": "array"
+                },
+                "message": {
+                  "type": "string"
+                }
+              },
+              "type": "object"
+            }
+          }
+        },
+        "summary": "Unshare a workflow with other users."
+      }
+    },
     "/api/workflows/{workflow_id_or_name}/workspace": {
       "get": {
         "description": "This resource retrieves the file list of a workspace, given its workflow UUID.",