The disclosure appears to buttress the company’s concerns that the dispute could pose a threat to encryption safeguards that goes well beyond the single California case.

Apple is fighting the government’s demands in at least seven of the other nine cases, Marc J. Zwillinger, a lawyer for the company, said in a letter unsealed in federal court on Tuesday.

“Apple has not agreed to perform any services on the devices,” Mr. Zwillinger wrote. Starting in December, the letter says, Apple has in a number of cases objected to the Justice Department’s efforts to force its cooperation through a 1789 statute known as the All Writs Act, which says courts can require actions to comply with their orders.