A law enforcement agency may not employ an individual as a police officer for a period not exceeding 1 year unless the individual is certified by the Commission. In this subsection, “nonfull-time police officer” means an individual who does not work in the law enforcement field at least 7 months during the calendar year. The certification requirements of subsection (a) of this section do not apply to the nonfull-time police officers of a law enforcement agency that: employs, during a calendar year, at least 70 full-time sworn police officers; and employs at least 100 nonfull-time police officers.