Any employee or officer who is employed on a full-time basis by the State, or a county, city or district thereof, who is paid a monthly or annual salary for his or her employment and whose public duty includes the practice of professional engineering or the practice of land surveying as defined in this chapter shall not engage in the private practice of professional engineering or the private practice of land surveying during the hours when he or she is required to perform his or her duties for the State, county, city or district.