Microsoft is suing the Department of Justice to demand the right to tell users when it gives officials access to personal data. The company says forcing it to keep such searches a secret is a double constitutional violation.

The case centers on the Electronic Communications Privacy Act, which dates back to 1986 and extends the existing rights and restrictions on government wiretaps to cover electronic communications.

Controversially, the law doesn’t just allow for warrants that force communications providers to give the government access to a customer’s data such as emails or online activity. It also provides for courts to add a stipulation that means the communications provider can’t then tell the customer concerned about the warrant or that their data has been made available.

In the government’s view, such stipulations are necessary as they prevent a suspect being tipped off about an investigation. Microsoft’s counter is that the situation should be compared with police searches of physical data such as the contents of a filing cabinet in the home. In those cases a warrant-based search would usually involve the suspect becoming aware of the search, leaving investigators to decide if the benefits of the search outweighed the suspect being tipped off.

Microsoft says it believes the number of warrants sought and issued for electronic searches is disproportionately higher than the number for physical searches, something it attributes to the option for secrecy. Of course, by definition it’s impossible to know if that’s true across all communications providers.

It also says such gag orders are often left without an expiry date, making them effectively indefinite, something Microsoft argues is excessive given that the secrecy should cover a specific risk.

The company is challenging the law on two constitutional points. It says indefinite gagging orders are a breach of the First Amendment because it has the right to tell the customers a fact (namely the existence of the search) “as soon as secrecy is no longer required.”

It also argues that gagging orders inherently violate the Fourth Amendment right for people to know their property is being searched.

The Wall Street Journal quotes a law professor who says the case may boil down to whether data stored “privately” on Microsoft servers should be likened to physical documents handed over to a third party, or to documents stored in the customers home.