Sources have told BuzzFeed that Twitter employees quietly filtered tweets with abusive language for a Q&A session with President Obama, and potentially in another session with celebrity Caitlyn Jenner. A "former senior Twitter employee" says that during a May 2015 #AskPOTUS event, then-CEO Dick Costolo told employees to use an algorithm to filter out abusive tweets, and another source says that a team also manually removed messages that slipped through.

The decision was allegedly made without telling higher-level members of Twitter, in order to avoid objections. But we may have seen a similar kind of filtering before. In 2014, an automated system appeared to be blocking anti-Semitic slurs tweeted at British Parliament member Luciana Berger. Although Twitter didn’t confirm the report at that time, it was a potentially troubling development for a platform that has both expressed a devotion to unfettered speech and notably failed at curbing harassment of non-famous users.

Former CEO Dick Costolo calls the claim 'total nonsense'

As another BuzzFeed source (along with a larger report on Twitter’s anti-abuse war) notes, the move could be an example of a "double standard" favoring high-profile users whose departure could seriously hurt Twitter’s public image. Earlier this summer, for example, Twitter banned the account of longtime troll Milo Yiannopoulos, but only after a major debacle involving Ghostbusters star Leslie Jones. Without further explanation or transparency, removing certain classes of tweets for specific users undercuts Twitter’s attempt to provide a wide platform for speech — while doing little to help the people who are most vulnerable to abuse.

Costolo responded obliquely calling the report "sensationalist nonsense" on Twitter. "Total nonsense and laughably false as anybody who would speak on the record would tell you. Absurd. Not even going to link to it," he wrote. He followed up with another tweet. "Shows a lack of understanding of the very basics of how trust and safety works at Twitter. Sensationalist nonsense."

Update 11:25am ET: Added statement from Dick Costolo.