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