Senator Roger Wicker sent letters to Apple Inc, Facebook Inc, Amazon.com Inc, Alphabet Inc and Twitter in which he said “thousands of conservative users’ accounts and content” have been “restricted or permanently removed from platforms.”

The companies took their strongest actions yet against President Donald Trump to limit his reach, fearing continued violence stemming from his posts after his supporters attacked the U.S. Capitol building last week.

Apple, Google and Amazon also suspended Parler – a pro-Trump app where users have threatened more violence – from their respective app stores and Web-hosting services, a set of moves that stand to severely handicap the service.

U.S President, Donald Trump

Wicker also sought explanation for the moves against Parler.

“Americans deserve transparency and accountability for what appears to be politically biased censorship – silencing the voices of users and public figures alike,” Wicker wrote.

Twitter said on Friday the company has received the letter and will be responding to it. Facebook pointed Reuters to founder Mark Zuckerberg’s comments explaining the ban on the president’s accounts. The other companies did not immediately respond to a requests seeking comment.

REUTERS