The city is accusing police officers of not handing out as many tickets as usual as a pressure tactic against Bill 3.
In late September, the Quebec labour relations board was asked by the City of Montreal to hold the police union to account for the loss in revenue.
Yves Francoeur, head of the brotherhood, said the union would fight the grievance.
This is not the first time the labour board has been asked to weigh in on Bill 3 pressure tactics.
Following a complaint by the city lodged against the firefighters for apparent slower response times earlier in September, the board ordered the firefighters to "take all necessary measures" to respond to all calls with no delay.