President Joe Biden has been urged to pardon Julian Assange by two US congressmen who warn they are “deeply concerned” the Wikileaks founder’s guilty plea deal sets a precedent for prosecuting journalists and whistleblowers with espionage offences.

James McGovern, a progressive Democrat from Massachusetts, and Thomas Massie, a libertarian Republican from Kentucky, wrote to the president with the bipartisan request to pardon the Australian publisher earlier in November.

The pair urged Biden to “send a clear message that the US government under your leadership will not target or investigate journalists and media outlets simply for doing their jobs”.

Assange was freed in June 2024 after pleading guilty to violating US espionage law, in a deal that allowed him to return home to Australia and brought an end to an extraordinary 14-year legal saga.

Assange was charged in connection with the publication of hundreds of thousands of leaked documents about the Afghanistan and Iraq wars, as well as diplomatic cables, in 2010 and 2011.

In a letter dated 1 November McGovern and Massie expressed “appreciation” that the criminal case had been resolved and an extradition request to the United Kingdom dropped, bringing “an end to Mr Assange’s protracted detention and [allowing] him to reunite with his family and return to his home country of Australia”.

But the pair said they were “deeply concerned” the deal required Assange, a publisher, to “plead guilty to felony charges”.

“Put simply, there is a long-standing and well-grounded concern that section 793 [of the Espionage Act], which criminalizes the obtaining, retaining, or disclosing of sensitive information, could be used against journalists and news organizations engaged in their normal activities, particularly those who cover national security topics.”

The pair noted that this risk had “informed the Obama administration’s decision not to prosecute Mr Assange” and that Assange’s case was “the first time the Act has been deployed against a publisher”.

They said they share the view of Jodie Ginsberg, the chief executive of the Committee to Protect Journalists, who reacted to the plea agreement by saying “while we welcome the end of his detention, the US’s pursuit of Assange has set a harmful legal precedent by opening the way for journalists to be tried under the Espionage Act if they receive classified material from whistleblowers”.

McGovern and Massie, who previously worked with other members of congress to call for the charges to be dropped, urged Biden to pardon Assange, arguing “a pardon would remove the precedent set by the plea”.

Assange’s brother Gabriel Shipton and wife Stella Assange are in the Australian capital, Canberra, this week and Shipton is returning to Washington in January as part of a Pardon Assange campaign urging Biden to take action before he leaves office.

The pair have asked the Australian prime minister, Anthony Albanese, who said before the plea deal that he had raised Assange’s case with Biden, to call for a pardon in his farewell phone call with Biden.

“By granting a pardon to Julian Assange, President Biden can not only correct a grave injustice but also send a powerful message that defending democracy and press freedom remains at the core of his presidency,” a petition for the campaign argues.