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Facebook, Google and Twitter are headed back to Washington next week to testify at a congressional hearing about alleged tech censorship.

Tech companies have faced accusations that they're censoring conservative speech on their platforms. The companies have denied the allegations in the past.

The hearing before the Senate Judiciary's subcommittee on the Constitution is scheduled for April 10 and is titled "Stifling Free Speech: Technological Censorship and the Public Discourse."

A Facebook spokesperson said Neil Potts, its public policy director, will be testifying. Twitter and Google didn't immediately respond to a request for comment.

A source familiar with the Senate hearing said Twitter and Google officials will also be attending.

The hearing will likely mark Potts' second congressional appearance next week. Facebook and Google officials are expected to appear before the House Judiciary Committee on April 9 to answer questions about the spread of white nationalism on their platforms.

Facebook's testimony before Congress comes as CEO Mark Zuckerberg calls for more government regulation, including rules around content moderation. Some advocacy groups have raised concerns, though, about the government deciding what social networks should keep up or pull down.

In an op-ed for The Washington Post published over the weekend, Zuckerberg said lawmakers often tell him the social network has too much power over speech and that he agrees.

"Regulation could set baselines for what's prohibited and require companies to build systems for keeping harmful content to a bare minimum," Zuckerberg wrote.