Twitter has made another move to isolate itself from rival social networks.
Tumblr users had been able to import their contacts from Twitter, quickly expanding their personal Tumblr network.
But that changed Wednesday when Twitter cut off Tumblr's access to its service.
"To our dismay, Twitter has restricted our users’ ability to “Find Twitter Friends” on Tumblr," Tumblr said. "Given our history of embracing their platform, this is especially upsetting."
"While we’re delighted by the response to our integrations with Facebook and Gmail, we are truly disappointed by Twitter’s decision."
Twitter declined to comment on the Tumblr action.
The microblogging social network previously cut off access to Instagram users. And in June, LinkedIn said Twitter was no longer allowing it to relay users' tweets to its social network.
In its blogs, Twitter has on several occasions said it was aiming to build a more "core Twitter consumption experience" for its users.