A bipartisan pair of American politicians is telling Britain’s most secretive court to stop hiding its handling of Apple’s legal fight against a government demand to break into its customers’ encrypted data, warning that Whitehall’s taste for secrecy is “needlessly” straining relations between the two allies.

The letter, shared with the Guardian ahead of being sent to the investigatory powers tribunal (IPT) on Friday, is signed by the Democratic senator Ron Wyden of Oregon and the Republican congressman Warren Davidson of Ohio.

The row dates back to January 2025, when the Home Office served Apple with a technical capability notice under the Investigatory Powers Act, which requires companies to assist law enforcement in providing evidence. The UK government demanded that Apple provide a mechanism to access encrypted iCloud backups worldwide, a call the company met by withdrawing its Advanced Data Protection encryption feature from UK users the following month. Apple’s challenge to that order at the IPT was later thrown out after the Home Office withdrew the original notice and issued a narrower one targeting only British users’ data.

“It is wholly inappropriate for a foreign executive body to attempt to dictate the distribution of powers within the US government, nor should it be permitted to use secrecy directives under the Investigatory Powers Act to frustrate Article I powers under the US Constitution,” the pair wrote.

The Home Office has been approached for comment.

In August this year, Apple lodged a fresh complaint at the tribunal challenging the government’s power to issue such notices at all, with a case-management hearing on how that claim will proceed now listed for this month – the very hearing the new letter is aimed at.

Wyden and Davidson also signed an earlier letter to the tribunal in March 2025, alongside other lawmakers, pressing for the case to be heard in public. That intervention appears to have had an effect: weeks later the IPT rejected the government’s attempt to keep the case entirely secret, ruling that the “bare details” of Apple’s claim, including the identities of the parties, could be made public after receiving representations that, the tribunal noted, “strongly argued in favour of open justice and against the proceedings taking place in secret”.

In the new letter, Wyden and Davidson write that Congress “is not only a co-equal branch of government, it is the First Branch”, and argue that no government can be allowed to place “its demands beyond the reach of legislative inquiry”. They accuse the Home Office of trying to use a foreign secrecy order to override the constitutional powers of the US legislature, after Apple told Congress it had been permitted to brief only the attorney general, the vice-president and their staff – but not lawmakers – about the dispute.

They argue that Britain’s own constitutional traditions hold that no government can place its actions beyond the reach of legislative scrutiny – the same principle, they say, the Home Office is now violating.

“The UK government,” they write, “cannot champion legislative oversight at home while using administrative gag orders to kneecap the constitutional authority of the US Congress.”