(b) In any proceeding in this Court in which the constitutionality of an Act of Congress is drawn into question, and neither the United States nor any federal department, office, agency, officer, or employee is a party, the initial document filed in this Court shall recite that 28 U. S. C. ??2403(a) may apply and shall be served on the Solicitor General of the United States, Room 5614, Department