Service of one individual, until the completion of the investigation authorized by Senate Concurrent Resolution 26, Eighty-first Congress, as an attorney or expert for the joint committee, in any business or professional field, on a part-time basis, with or without compensation, shall not be considered as service or employment bringing such individual within the provisions of section
281,
283, or
284 of title
18, or of any other Federal law imposing restrictions, requirements, or penalties in relation to the employment of persons, the performance of services, or the payment or receipt of compensation in connection with any claim, proceeding, or matter involving the United States.