Yes, they can do this. 1) Your salary may seem or feel "confidential" to you, but it actually is not: an employer may generally share this information if it chooses; 2) nothing about your salary is protected against disclosure in a legal proceeding--regardless of where the court is located--so long as the proper rules and procedures are followed in requesting (e.g. a subpoena is issued in cooperation with and through a local U.S. court system (state or federal)). You cannot hide your employer's salary data or prevent its release.