(a) Violation of law. No former officer or employee of the U.S. Government, of any independent agency of the United States, or of the District of Columbia, may represent anyone in any matter administered by the Bureau if the representation would violate any of the laws of the United States.

(b) Personal and substantial participation. No former officer or employee of the executive branch of the U.S. Government, of any independent agency of the United States, or of the District of Columbia, may represent anyone with repect to any matter under the administration of the Bureau, if he or she participated personally and substantially in that matter as a Government employee.

(c) Official responsibility. No former officer or employee of the executive branch of the U.S. Government, of any indepenednt agency of the United States, or of the District of Columbia, may within one year after his or her employment has ceased, appear personally as a practitioner before the Bureau with respect to any matter administered by the Bureau if that representation involves a specific matter under the former employee's official responsibility as a Government employee, within a one-year period prior to the termination of that responsibility.

(d) Aid or assistance. No former officer or employee of the Bureau, who is eligible to practice before the Bureau, may aid or assist any person in the representation of a specific matter in which the former officer or employee participated personally and substantially as an officer or employee of the Bureau.