A subpoena (issued under 18 U.S.C. § 2703(d)) or court order is required to compel the disclosure of user account records (defined in 18 U.S.C. § 2703(c)(2)).
A search warrant--whether issued through the procedures in the Federal Rules of Criminal Procedure or through equivalent state warrant procedures upon a showing of probable cause-- is required to compel disclosure of the stored contents of an account.