37 CFR §11.10

1. (a)Only practitioners registered under § 11.6; individuals given limited recognition under § 11.9(a) or (b) or § 11.16; or individuals admitted pro hac vice as provided in § 41.5(a) or 42.10(c) of this chapter are permitted to represent others before the Office in patent matters.
2. (b)Post employment agreement of former Office employee. No individual who has served in the patent examining corps or elsewhere in the Office may practice before the Office after termination of his or her service, unless he or she signs a written undertaking agreeing:
   1. (1)To not knowingly act as an agent, attorney, or design patent practitioner for or otherwise represent any other person:
      1. (i)Before the Office,
      2. (ii)In connection with any particular patent or patent application,
      3. (iii)In which said employee participated personally and substantially as an employee of the Office; and
   2. (2)To not knowingly act within two years after terminating employment by the Office as agent, attorney, or design patent practitioner for, or otherwise represent any other person:
      1. (i)Before the Office,
      2. (ii)In connection with any particular patent or patent application,
      3. (iii)If such patent or patent application was pending under the employee's official responsibility as an officer or employee within a period of one year prior to the termination of such responsibility.