During hearings on Capitol Hill, Senate and House Republicans and Democrats applauded efforts by Facebook and Twitter to root out foreign election meddling. But they warned that regulation may loom for social media companies, which are largely unfettered by the kinds of rules that govern other large consumer companies.

Pressure increased on Silicon Valley – and on Facebook in particular – after damaging revelations about Russian-backed influence operations and the Cambridge Analytica data collection scandal. Executives have signed off on the Honest Ads Act, which would mandate more transparency about who runs political ads on social media services.

Facebook and Twitter are gearing up to influence what kind of regulation gets enacted as they face threats from Washington to weaken a law, known as Section 230 of the Communications Decency Act, that shields internet companies for the content that people put on their platforms.

“We don’t think it’s a question of whether regulation,” Facebook’s Chief Operating Officer Sheryl Sandberg testified during a congressional hearing. “We think it’s a question of the right regulation.”

During Wednesday’s hearing before the Senate Intelligence Committee on foreign election interference that ran more than 2 1/2 hours, lawmakers questioned Twitter’s chief executive Jack Dorsey and Sandberg over their companies’ efforts to disrupt foreign influence campaigns and the spread of disinformation on their platforms. They warned companies’ efforts were falling short before November’s midterm elections as social media users continue to be targeted by foreign actors seeking to exacerbate political divisions in the USA.

“Congress is going to have to take action here,” Sen. Mark Warner, D-Va., warned. “The era of the Wild West in social media is coming to an end. Where we go from here is an open question.”

He said, “The size and reach of your platforms demand that we, as policymakers, do our job, to ensure proper oversight, transparency and protections for American users and for our democratic institutions.”

“If the answer is regulation, let’s have an honest dialogue about what that looks like,” said Sen. Richard Burr, R-N.C., chairman of the Senate Intelligence Committee.

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Most alarming to the tech industry is any discussion of further weakening Section 230 protections. Georgetown University’s Larry Downes, project director of the Center for Business and Public Policy, who specializes in regulation, internet and technology policy, said any such move by Washington would be “the scorched earth approach.”

“Removing more of the platforms’ immunity from liability for illegal third-party content, including fraud and libel, would result in drastic reductions in the kinds of content companies would be able to host, notably social networks. It might, as in Europe, make such services effectively impossible,” Downes said.

That Section 230 was raised in two congressional hearings Wednesday shows how sharply the political climate for technology companies in Washington has changed.

Within minutes of the Senate hearing wrapping up, U.S. Attorney General Jeff Sessions announced he would meet with several state attorneys general to discuss whether social media companies are “intentionally stifling” free speech and obstructing competition. The remarks escalate charges of anti-conservative bias by President Donald Trump and Republican lawmakers. Last week, Trump blasted Google, alleging it muzzles conservative voices.

Dorsey also appeared before a House Energy and Commerce Committee meeting where Republicans sounded the alarm about conservatives being excluded from the auto-fill feature of Twitter’s search and other instances of alleged bias.

“Out of the more than 300 million active Twitter users, why did this only happen to certain accounts?” House Energy and Commerce Committee Chairman Greg Walden, R-Ore., asked Dorsey.

Democrats pushed back on the charges of conservative bias. New Jersey Rep. Frank Pallone, the top Democrat on the committee, accused Republicans of trying to rally the base and raise funds “by fabricating a problem that simply does not exist.”

Twitter shares fell 6 percent Wednesday after Dorsey testified in the Senate hearing that there would have to be “massive shifts” in how Twitter and other social media companies operate. Facebook shares closed down 2 percent.

In a blog post Tuesday timed to the hearings, Federal Communications Commission chief Ajit Pai said Facebook, Google and Twitter offer users too little information into how they work.

“The public deserves to know more about how these companies operate,” he wrote. “And we need to seriously think about whether the time has come for these companies to abide by new transparency obligations.”

Google’s absence from Wednesday’s hearing was repeatedly condemned by senators. Sen. Kamala Harris, D-Calif., referred to Google as “the invisible witness,” represented by an empty chair.

The Senate committee invited Larry Page, chief executive of Google’s parent company Alphabet, but Google declined, offering to send  Kent Walker, its senior vice president for global affairs and a point person on election interference. The committee rejected that.