The ballot mentioned a "lack of planning to increase staffing" to protect the public. Lock says he didn't know anything about the vote and had no reaction.
The Flint police union says Chief Alvern Lock got a no-confidence vote from 85 percent of officers who cast a ballot.
Mayor Dayne Walling disagrees with the union's position and calls Lock one of the Flint's hardest-working employees.
There has been tension between Flint officers and city officials. Kevin Smith's full-time job as a union leader was eliminated in March, and he was put on patrol. The union also has sued over pay cuts and longer shift hours.