The United States shall be represented on the two commissions by a total of not more than four United States Commissioners, who shall be appointed by the President, serve as such during his pleasure, and receive no compensation for their services as such Commissioners. Individuals serving as such Commissioners shall not be considered to be Federal employees while performing such service, except for purposes of injury compensation or tort claims liability as provided in chapter
81 of title
5 and chapter
171 of title
28. Of such Commissioners—