A Government employee may not (other than on behalf of the United States) serve as an expert witness, with or without compensation, in any proceeding before a court or agency of the United States in which the United States is a party or has a direct and substantial interest unless authorized to do so. (Link to 5 CFR 2635.805 for more information)
However, this prohibition applies to SGEs only if they have participated as Government employees in the particular proceeding or in the particular matter that is the subject of the proceeding. This prohibition is in place during the entire time of their appointment (not just when they are working as SGEs).
A more restrictive standard applies to a smaller class of SGEs who:
- Are appointed by the President or
- Serve on a commission established by statute or
- Have served or are expected to serve more than 60 days in a period of 365 consecutive days
For these SGEs, the restriction applies to any proceeding in which the SGE's own agency is a party or has a direct and substantial interest.