A Senate committee voted Thursday to authorize subpoenas that could force the chief executives at Facebook, Google and Twitter to testify at an upcoming congressional hearing, escalating lawmakers’ war with Silicon Valley over their policies to police content online.

The vote gives the Senate Commerce Committee the power to compel the testimony of Facebook’s Mark Zuckerberg, Google’s Sundar Pichai and Twitter’s Jack Dorsey if they don’t agree to submit to questioning voluntarily. It marks a surprising bipartisan rebuke of the tech industry on the part of lawmakers long faulted for failing to hold top executives to account for their business practices.

“These CEOs can make time to spend a few hours with the committee,” said Republican Sen. Roger Wicker (Miss.), the committee’s chairman, citing the need to explore the tech giants’ efforts to oversee “Americans’ speech at a critical time in our democratic process.”

Even as they voted to approve the subpoenas, Democrats still expressed early concern that the hearing threatened to devolve into a political affair, allowing Republicans to attack social media sites ahead of the 2020 presidential election.

In recent weeks, Facebook and Twitter have sought to discipline President Trump for publishing false or dangerous content on their services, including posts that seek to cast doubt on mail-in voting. Trump and his allies have responded by assailing Silicon Valley over allegations that their actions amount to a form of political censorship — a charge they and others strongly deny.

“This appears to me like an attempt to work the refs coming up to the election, and I sincerely hope to be proven wrong,” said Sen. Brian Schatz (D-Hawaii), who along with fellow Democrats urged the committee to focus most of its attention on issues including antitrust.

Party lawmakers initially signaled they opposed a subpoena, but they dropped their opposition after working out an agreement with Republicans to ensure the scope of the hearing would touch on privacy and the effects of the tech industry on local journalism.

Google did not respond to a request for comment, and Facebook and Twitter declined to comment.

Wicker sought the three companies’ testimony as part of a broader look at Section 230, the portion of federal law that spares tech giants from being held liable for a wide array of activities — including the way they moderate their sites and services.

Democrats and Republicans alike question if the industry’s decades-old legal shield has outlived its usefulness, and some even have banded together to unveil a flurry of legislative proposals in recent months to overhaul it. Many lawmakers say that the protections offer Web users little recourse when Facebook, Google and Twitter allow election misinformation, hate speech and other harmful content to go viral online.

But their loose consensus increasingly seems in jeopardy, as GOP lawmakers in particular continue to contend that Section 230 allows Facebook, Google and Twitter to censor conservatives online with impunity — a charge for which they have offered no evidence, and one the industry strongly denies.

On Thursday, Wicker again raised allegations that social media sites had engaged in “suppression of certain viewpoints” online, essentially “stifling the true diversity of political discourse on the Internet.” The comments triggered some trepidation among panel Democrats, led by Washington Sen. Maria Cantwell, who urged her colleagues about the “chilling effect” their inquiry might have on the tech giants’ efforts to police their platforms. Many Democratic lawmakers instead suggested the panel instead hold its hearing with Facebook’s, Google’s and Twitter’s leaders after the November election.

The inquiry comes as the White House and Justice Department similarly have escalated their campaign to whittle down the tech industry’s prized legal shield. Earlier this year, Trump signed a highly controversial executive order that could pave the way for federal regulators to oversee political speech on the Internet. And the administration in September sought to encourage state attorneys general specifically to probe allegations of political bias.