Facebook Inc. dismantled a popular anonymous discussion board for employees last year that had become a forum for conservative political debate that sometimes degenerated into racist or sexist comments, people familiar with the matter said, a rare move to censor speech internally.

FB Anon, the name of the forum shut down in December and reported on Wednesday, became a hub for employees who backed Donald Trump’s candidacy, the people said. Before the election, the group put up posters across campus that read “Trump Supporters Welcome.”

But FB Anon also attracted comments that many employees found offensive, the people said. For example, some posts last year said Facebook lowered the bar to attract female engineers to boost its diversity numbers, one of the people said, provoking angry responses from others in the chat room.

“A cornerstone of our culture is being open,” said Lori Goler, Facebook’s head of people, in a statement Wednesday. “The FB Anon internal Facebook group violated our terms of service, which require people who use Facebook (including our employees) to use an authentic identity on our platform.”

In explaining the decision in early 2017, Chief Executive Mark Zuckerberg told employees that FB Anon contained harassing messages, according to one of the people.