The Senate Commerce Committee will vote on whether to subpoena the chief executive officers of Google, Facebook and Twitter because they have declined testify on a legal shield that protects online platforms against lawsuits, a committee spokesperson said.

The vote to issue subpoenas for Sundar Pichai of Google, Mark Zuckerberg of Facebook and Twitter’s Jack Dorsey will take place on October 1, the committee said on Thursday afternoon. On Thursday night, the spokesperson, Alexis DeJarnette, said all three executives had refused to appear.

Earlier, senator Maria Cantwell of Washington, called the subpoena threat a “partisan effort 40 days before an election”. “Taking the extraordinary step of issuing subpoenas is an attempt to chill the efforts of these companies to remove lies, harassment and intimidation from their platforms,” she said in an emailed statement.

Under committee rules, if the ranking member doesn’t agree to a subpoena request from the chairman, the chairman can call for a full committee vote on the matter.

The panel wants the men to address Section 230 of the Communications Decency Act, which allows the platforms to avoid lawsuits over content that their users post, according to another committee spokesperson, who was granted anonymity to discuss the proceedings.

The legal shield has increasingly come under attack in Washington. The justice department on Wednesday unveiled its latest proposal to overhaul the law. The Federal Communications Commission is also considering changes via a rulemaking requested by President Donald Trump in response to Twitter’s fact-checking of some of his posts.