Workplace chat company Slack said today it’s removed 28 accounts for having a “clear affiliation with known hate groups.” The announcement, posted as a message to its website this morning, is a rare admission from the company that its platform can and has been used as a way to organize hateful groups of users, some of which may in the future take real-world violent action. Slack competitor Discord has a history of taking similar action against such groups over the past few years, starting with the banning of servers promoting neo-Nazi ideologies in 2017.

Numerous other online platforms have taken action against hate speech and groups that propagate and organize around it, including not just Discord, but Facebook, Google, GoDaddy, GoFundMe, Reddit, Uber, YouTube, and many others. A turning point for a number of these companies was the August 2017 white supremacist rally in Charlottesville, Virginia that resulted in the murder of counter-protestor Heather Heyer. Since then, tech platforms have taken harsher stances around hate speech, especially when it involves the organizing of groups with reputations for showing up to protests and rallies.

Slack, however, has remained notably absent from the conversation, perhaps because its platform is geared toward businesses and not necessarily designed, like Discord’s, to allow for large-scale, semi-public chat rooms. Still, Slack says it has policies that ban using its product for “illegal, harmful, or other prohibited purposes.”

In this case, what’s more interesting is that it’s not entirely clear how Slack discovered these accounts, what type of organizing these accounts were engaging in, and what raised red flags for whatever division inside Slack is responsible for handling these investigations. In a follow-up statement, a company representative told The Verge, “We don’t normally comment on how we conduct our investigations, but we want to be clear that the privacy of our customer data is sacrosanct. In this case, we were informed of the possible use of Slack by hate groups and we were able to determine their affiliation on an organizational level.”

Here’s the initial announcement on the subject in full:

Today we removed 28 accounts because of their clear affiliation with known hate groups. The use of Slack by hate groups runs counter to everything we believe in at Slack and is not welcome on our platform. Slack is designed to help businesses communicate better and more collaboratively so people can do their best work. Using Slack to encourage or incite hatred and violence against groups or individuals because of who they are is antithetical to our values and the very purpose of Slack. When we are made aware of an organization using Slack for illegal, harmful, or other prohibited purposes, we will investigate and take appropriate action and we are updating our terms of service to make that more explicit.

Update 3/19, 4PM ET: Added follow-up statement from Slack.