Google has refused to deny receiving a secret legal order from the British government, according to a bipartisan group of members of Congress who are concerned Westminster may have demanded that several U.S. technology companies provide its security services with a mechanism to access encrypted messages.

It follows the British government reportedly issuing such a secret legal demand, officially known as a Technical Capability Notice (TCN), to Apple. Apple is believed to be contesting the demand at a closed court hearing on Friday.

In a letter published Thursday, the members of Congress complained about the secrecy of this court hearing, arguing it “impedes Congress’s power to conduct oversight, including by barring U.S. companies from disclosing foreign orders that threaten Americans’ privacy and cybersecurity.”

Despite widespread reporting of the TCN issued to Apple, the company is prohibited from confirming whether it had received such an order under the U.K.’s Investigatory Powers Act. In their letter, the members of Congress wrote that Apple had informed them “that had it received a technical capabilities notice, it would be barred by U.K. law from telling Congress whether or not it received such a notice.”

Companies who have not received such a notice are obviously free to state so.

“Google also recently told Senator [Ron] Wyden’s office that, if it had received a technical capabilities notice, it would be prohibited from disclosing that fact,” wrote the group.

Experts, including from Britain’s own intelligence community, have said that the government’s attempts to access encrypted messaging platforms should be more transparent. Academics described the Home Office's ongoing refusal to either confirm or deny the legal demand as unsustainable and unjustifiable.