(a) A Department employee may not testify as an expert or opinion witness for any other party other than the United States.

(b) Whenever, in any legal proceeding involving the United States, a request is made by an attorney representing or acting under the authority of the United States, the General Counsel, or the Solicitor, or appropriate agency counsel will make all necessary arrangements for the Department employee to give testimony on behalf of the United States. Where appropriate, the General Counsel, or the Solicitor, or appropriate agency counsel may require reimbursement to the Department of the expenses associated with a Department employee giving testimony on behalf of the United States.