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Elon Musk’s social media company X has asked the Supreme Court to shield its users from US law enforcement, intervening in a case that could force the federal government to produce a warrant to access private data.

In a brief filed to the high court, X said it was concerned about “broad, suspicionless” requests, adding that platforms should “not be coerced into helping governments undermine their users’ privacy”.

The supporting brief, filed on Friday, comes in a long-running case brought by James Harper, a user of crypto exchange Coinbase. He claims he was one of thousands of Coinbase clients whose trading data was handed to the Internal Revenue Service as part of a “fishing expedition” by the agency into potential tax fraud, in violation of the site’s privacy policies.

A win for the plaintiff in the case, which the Supreme Court has not yet agreed to hear, would restrict the US government — of which Musk is a part — from compelling data to be handed over by X without “probable cause and particularised suspicion”. 

X, which was bought on Friday by Musk’s artificial intelligence company xAI, declined to comment on the filing.

A person close to X said Harper’s case “raises a concern that [X] users’ speech might be curtailed if the government is allowed to have access to users’ data without a court-approved search warrant”.

They added: “This issue is not specific to X. It means that the constitution does not prevent the government from snooping through any user’s account on any social media platform or financial platform.”

The timing of the intervention by X — the only individual corporation to have filed a brief in the case to date — is notable given the Trump administration’s use of public material on social media to vet migrants.

The Department of Homeland Security last month proposed broadening the collection of social media account handles from visa applicants and those wishing to apply for residence in the US. 

A White House spokesman did not respond to a request for comment.

X’s filing in the Supreme Court case also comes as Musk has taken an increasingly combative approach to what he claims have been government efforts globally to censor social media users.

Since buying X for $44bn in 2022, the self-proclaimed “free speech absolutist” has attacked “takedown” requests in Brazil, India and Australia, clashing with governments and judiciary in those countries.  

In the Harper case, X appears to be concerned that US government agencies could obtain users’ private records, using a legal doctrine that gives law enforcement a right to access information shared by an individual with third parties, even if no warrant has been issued.

“If Tony Soprano makes an ‘arrangement’ with a ‘business associate’, any collateral promises are unenforceable, including promises to keep it a secret,” X’s lawyers wrote, referring to the mob boss in the HBO TV drama The Sopranos.

“But terms of service agreements between users and Coinbase or X Corp would not be deemed illegal contracts, merely because some users . . . are otherwise properly subject to government investigation.”

X collects financial data from brands that advertise on its platform as well as users who offer or sign up to paywalled content.

The platform is looking to push further into financial services. Lawyers for X pointed out in the brief that chief executive Linda Yaccarino recently announced plans to launch X Money, a digital wallet and peer-to-peer payment service, with Visa as its first partner.

X’s brief was filed by lawyers at the Pacific Legal Foundation, a decades-old public interest law firm that fights for civil liberties. Its staff have previously criticised Musk on other matters.

Chris Giancarlo, a lawyer at Willkie Farr, whose firm is representing another supporter of the plaintiff in the case pro bono, said the Supreme Court decision “could have a lasting effect on the standards by which the government may access customers’ private information on crypto exchanges and other platforms without probable cause”.