Republican senators led by Ted Cruz in a letter Thursday suggested Twitter may be violating U.S. sanctions by letting Iranian leaders maintain accounts, which they asked company CEO Jack Dorsey to ban.

The big picture: Twitter has become a major political target for Cruz and other Republicans, who claim the company and other Silicon Valley giants are biased against conservatives and the Trump administration.

"While the First Amendment protects the free speech rights of Americans – and Twitter should not be censoring the political speech of Americans – the Ayatollah enjoys zero protection from the United States Bill of Rights," the senators wrote.

Details: The White House in June announced sanctions against top officials in Iran, including Supreme Leader Ayatollah Ali Khamenei and Iranian Foreign Minister Mohammad Javad Zarif.

The senators argue the sanctions prohibit American companies from providing goods or services to the officials, including internet-based services, and note that both have Twitter accounts.

"We therefore call on you to comply with those sanctions by ceasing the provision of services to Khamenei, Zarif, and any other designated Iranian entity," the senators said.

Sens. Tom Cotton, Marsha Blackburn and Marco Rubio signed the letter, which was also sent to President Donald Trump, Treasury Secretary Steven Mnuchin, Attorney General Bill Barr, and the U.S. Attorney for the Northern District of California.

Twitter declined to comment on the letter.

The catch: Twitter has long maintained that it's in the public interest for political figures to be permitted to speak on the platform, even if people find that speech objectionable. The company has used that same line of reasoning to explain why it hasn't cracked down on Trump despite tweets that seem to break platform rules such as a ban on targeted harassment.