From Google

Requests from US government agencies in civil, administrative, and criminal cases

The Fourth Amendment to the US Constitution and the Electronic Communications Privacy Act (ECPA) restrict the government’s ability to force a provider to disclose user information. US authorities must at least do the following:

In all cases: Issue a subpoena to compel disclosure of basic subscriber registration information and certain IP addresses

In criminal cases Get a court order to compel disclosure of non-content records, such as the To, From, CC, BCC, and Timestamp fields in emails Get a search warrant to compel disclosure of the content of communications, such as email messages, documents, and photos

https://policies.google.com/terms/information-requests?hl=en-US