Experts and consultants or organizations thereof may, as authorized by section
3109 of title
5, be employed by the President for the performance of functions under this chapter, and individuals so employed may be compensated at rates not in excess of the per diem equivalent of the highest rate payable under section
5332 of title
5, and while away from their homes or regular places of business, they may be paid actual travel expenses and per diem in lieu of subsistence and other expenses at the applicable rate prescribed in the Standardized Government Travel Regulations, as amended from time to time, while so employed: Provided, That contracts for such employment may be renewed annually.