Mich. Comp. Laws § 38.506
For the benefit of the public service and to prevent delay, injury, or interruption therein by reason of the enactment of this act, all persons holding a position in the fire and/or police department, including the chief thereof, when this act takes effect, who shall have served in such position for a period of at least 6 months last past continuously, are hereby declared eligible for permanent appointment under civil service to the offices, places, positions or employments which they shall then hold, respectively, without examination or other act on their part, and not on probation; and every such person is hereby automatically adopted and inducted permanently into civil service, into such office, place, position or employment which such person then holds as completely and effectually to all intents and purposes as if such person had been permanently appointed thereto under civil service after examination and investigation: Provided, however, That any employee with less than 6 months' service shall be classed as probationer under this act.
MCL 38.506