Alphabet’s YouTube has banned six channels known to promote white supremacist content — including those of David Duke, Stefan Molyneux and Richard Spencer — escalating the company’s efforts to root out hate speech and respond to recent criticism of the video site.

The company said the channels violated its policies by claiming members of protected groups were inferior. Duke is the former grand wizard of the Klu Klux Klan, while Molyneux and Spencer consider themselves philosophers.

YouTube, like many of its peers in Silicon Valley, is stepping up efforts to crack down on hate speech in response to growing outcry about such content on social media. The business, which is part of Google, updated its hate speech policy about a year ago, and prohibits any content that promotes violence or hatred among individuals or groups based on factors such as age, race and gender.

Earlier Monday, Reddit banned several message boards for encouraging hate, and Amazon.com’s video streaming site Twitch suspended President Donald Trump’s account for reposting a speech in which he characterized Mexican immigrants as rapists. Facebook has also enacted new hate speech rules as it faces an advertiser boycott over its policies.

YouTube has wrestled with how best to respond to inflammatory and offensive videos posted by provocateurs like Molyneux and Spencer, who have amassed huge followings on the world’s largest video site. Tech companies say they are not responsible for the views posted by their users, and only take down videos that violate their policy guidelines.

On Twitter, Molyneux and Spencer decried the move for infringing upon their speech, and retweeted followers criticizing the platform.