A Senate panel voted Thursday to subpoena the chief executive officers of Facebook Inc., Alphabet Inc.’s Google, and Twitter Inc. to testify on a legal shield that is key to their online platforms’ business models.

The Senate Commerce Committee moved to compel appearances by Mark Zuckerberg, Sundar Pichai and Jack Dorsey after failing to reach agreements with the companies to send the CEOs voluntarily.

The vote is part of increasing bipartisan concern in Washington about the power of the technology giants, in particular ahead of the November presidential election. The committee is also planning to ask the CEOs about a federal privacy law and media consolidation.

The panel’s GOP chairman, Senator Roger Wicker, wants the executives to address possible changes to a law known as Section 230 of the Communications Decency Act. The provision, which protects the companies from lawsuits over user content, is increasingly under fire from lawmakers on both sides of the aisle.

“On the eve of a momentous and highly charged election it is imperative that this committee of jurisdiction and the American people receive a full accounting from the heads of these companies on their content moderation practices,” Wicker said before the vote.