4 Pa. Code § 7.156
No employe, appointee or official in the Executive Branch of the Commonwealth shall engage in or accept private employment or render services for a private interest unless such employment or service is approved in advance by the Head of the Agency to which the affected person is assigned. Supplementary employment may be undertaken only when not in conflict with the conditions of employment regulations promulgated by the Executive Board and, if applicable, the Civil Service Commission. Furthermore, supplementary employment may be undertaken only when not in conflict with the conditions of employment or regulations promulgated by the government agency by which such official or employe is employed. This section shall not prohibit individuals appointed to serve part time on Boards and Commissions from pursuing their usual occupation; however, they will not perform services or receive compensation from persons or institutions which they regulate or otherwise conduct themselves in a manner inconsistent with the impartial administration of their official duties.
4 Pa. Code § 7.156
This section cited in 4 Pa. Code § 7.159 (relating to enforcement).