image captionTwitter’s Jack Dorsey, Facebook’s Mark Zuckerberg and Google’s Sundar Pichai have been told to give testimony
The US Senate Commerce Committee has voted to subpoena the heads of Google, Facebook, and Twitter.
It means that Sundar Pichai, Mark Zuckerberg and Jack Dorsey face being quizzed by senators about their policies on different types of content.
One focus will be the legal protections they enjoy regarding what they leave up and take down on their platforms.
They are also likely to be challenged over controversies about privacy and misinformation.
Republicans and Democrats on the committee voted unanimously to summon the chief executives.
However, each side is likely to have different priorities - with some Republican members speaking about the alleged censorship of conservative views online, while Democrats focus on competition and misinformation.
“There has never been such an aggregation of power in the history of humankind as big tech enjoys today, with money and monopoly, power and the hubris that comes with the unchecked use of power,” Republican Senator Ted Cruz said following the vote.
Currently, social media platforms and other websites are protected from prosecution under Section 230 of the Communications Decency Act.
It means, in effect, that the platforms are not liable for what is posted by their users if they take things down once notified, unlike traditional newspaper publishers.
Democrats on the Commerce Committee had initially objected to their Republican colleagues’ use of the subpoena power, but changed their minds for the vote on Thursday after the scope of the discussion was widened.
The three chief executives had initially been invited to attend voluntarily, but declined.
The fresh summons is the latest regulatory headache for the tech giants, who face a raft of critical decisions by authorities in the coming weeks.
July’s congressional hearing with the companies, plus Amazon, dealt with anti-trust issues, including allegations that they had deliberately eliminated smaller rivals in a quest for market dominance.
The congressional report into that event is expected to be published next week.
The US Department of Justice is understood to be in discussions with state attorneys general over a potential anti-trust case against Google over its practices - a legal action which could also begin as early as next week.
And similar actions are being pieced together abroad.
The European Union’s draft version of a forthcoming law reportedly bans tech giants from giving their own products preferential treatment.
The draft of the Digital Services Act, seen by a number of news outlets, says that big tech “gatekeepers” may have to share user data with rivals to create an even playing field in some circumstances.
US sanctions on Huawei on national security grounds have created a challenge for the company - one of the world’s biggest phone manufacturers - which says it will begin using its own non-Android operating system next year.
That decision is also expected this month.