Google issued new guidelines limiting employee discussion of politics and other topics not related to work, in a major shift for a company that has long prided itself on open debate and a freewheeling internal culture.

The Alphabet Inc. unit said in a public memo on Friday that staffers should avoid spending time hotly debating matters unrelated to their jobs and refrain from name-calling, among other discouraged behavior. Google also said it would appoint employees to moderate the company’s famously raucous internal message boards, rather than allowing volunteers to do so—in effect acknowledging that the discussions have spiraled out of control.

“This follows a year of increased incivility on our internal platforms, and we’ve heard that employees want clearer rules of the road on what’s OK to say and what’s not,” a Google spokeswoman said.

The new policy represents a significant about-face for Google. The tech titan helped pioneer the Silicon Valley idea of the workplace as a college-like campus where employees can express themselves freely on topics that are important to them.

The company’s internal message boards host thousands of discussion groups, on topics ranging from social issues to sports, and employees can spend hours a day sparring in them. In recent years, though, the level of debate at times has driven a wedge between staffers with opposing views as well as between management and an increasingly activist workforce.