The U.S. Senate Commerce Committee on Thursday unanimously voted to approve a plan to subpoena chief executives of Twitter, Alphabet's Google and Facebook for a hearing likely to be held before the election on a prized legal immunity enjoyed by internet companies.

The hearing will discuss reforming Section 230 of the Communications Decency Act, which offers tech companies protection from liability over content posted by users.

The panel's top Democrat Maria Cantwell, who opposed the move last week, saying she was against using "the committee's serious subpoena power for a partisan effort 40 days before an election," changed her mind and voted to approve the move.

"I actually can't wait to ask Mr. Zuckerberg further questions," Cantwell said. "I welcome the debate about 230."

The committee, chaired by Republican Senator Roger Wicker, had originally asked the executives to come on Oct. 1 on a voluntary basis and was ready to issue subpoenas last week.

On Thursday, he said Section 230's "sweeping liability protections" are stifling diversity of political discourse on the internet.

"After extending an invite to these executives, I regret that they have again declined to participate and answer questions about issues that are so visible and urgent to the American people," Wicker said.

Republican President Donald Trump has made holding tech companies accountable for allegedly stifling conservative voices a theme of his administration. As a result, calls for a reform of Section 230 have been intensifying ahead of the elections, but there is little chance of approval by Congress this year.

Last week Trump met with nine Republican state attorneys general to discuss the fate of Section 230 after the Justice Department unveiled a legislative proposal aimed at reforming the law.

The chief executives of Google (GOOGL), Facebook (FB), Apple Inc. (AAPL) and Amazon.com Inc. (AMZN) recently testified before the House of Representatives Judiciary Committee's antitrust panel. The panel, which is investigating how the companies' practices hurt rivals, is expected to release its report as early as next Monday.