The United States government, still entangled with Apple in the battle over an encrypted iPhone, has taken on another big opponent in its efforts to access encrypted communications: WhatsApp.

The hyper-popular mobile messaging app is, in some parts of the world with poor phone coverage, the default communications mechanism. Now owned by Facebook, WhatsApp employs end-to-end encryption for its messages, and that feature has frustrated the Department of Justice in a case in which it has a wiretap order for WhatsApp messages, according to the New York Times. Although it has the order, the government can’t get access to the messages in question because WhatsApp doesn’t have the cleartext versions of them.

The case is similar, but not identical, to the Apple dispute. In the Apple dispute, the FBI is fighting to get access to encrypted data that is housed on the iPhone 5C used by Syed Farook, one of the alleged San Bernardino shooters. Apple has turned over the unencrypted data that it has, but the FBI wants the company to build a custom, backdoored version of iOS to install on the iPhone to allow the agency to bypass the security passcode and access the phone’s data. Apple has refused to comply with the order thus far.

But in the WhatsApp case, the government reportedly wants access to messages exchanged between users, and those messages are encrypted during transit. That means the company doesn’t have unencrypted copies of the messages, and the wiretap order that the government has for the case isn’t of much use at the moment.

“WhatsApp is, of course, unable to provide decrypted text in response to the wiretap order, just as it was unable to comply with a similar order by a Brazilian court earlier this month. The whole point of end-to-end encryption is that no one but the intended recipient of a message is able to decipher it,” Nate Cardozo, a staff attorney at the EFF, said.

Right now, the government doesn’t appear to have gone to court asking for a second order–as it has in the Apple case–compelling WhatsApp to comply with the wiretap order. If that happened, it would be on different legal grounds than the Apple order, Cardozo said.

“Presumably, that second order would look similar to the San Bernardino order and direct WhatsApp to write code that would break its own encryption and allow it to provide plain text in response to the wiretap order,” Cardozo said.

“If the government decides to seek that second order against WhatsApp, it would almost certainly be grounded, not in the All Writs Act but in the ‘technical assistance’ provision of theWiretap Act.”

The Times report does not specify what kind of investigation the WhatsApp case concerns.

Image from Flickr stream of Sam Azgor.