((a)) Members of the Commission who are Members of Congress, officers of the executive branch of the Federal Government, Governors, or full-time salaries officers of city and county governments shall serve without compensation in addition to that received in their regular public employment, but shall be allowed necessary travel expenses (or, in the alternative, a per diem in lieu of subsistence and mileage not to exceed the rates prescribed in subchapter I of chapter 57 of title 5), without regard to subchapter I of chapter 57 of title 5, the Standardized Government Travel Regulations, or , and other necessary expenses incurred by them in the performance of duties vested in the Commission.
((b)) Unless prohibited by State or local law, members of the Commission, other than those to whom subsection (a) is applicable, shall receive compensation at the rate of $50 per day for each day they are engaged in the performance of their duties as members of the Commission and shall be entitled to reimbursement for travel, subsistence, and other necessary expenses incurred by them in the performance of their duties as members of the Commission, as provided for in subsection (a) of this section.