Victorian police could be paid out hundreds of millions of dollars in overtime if union-led court action is successful.
At stake, is unpaid work by thousands of officers at the beginning and end of each shift over the past six years, according to Police Association secretary Wayne Gatt.
The union launched proceedings in the Federal Court on Wednesday demanding Victoria Police repay the wages for current and former officers.
The claim relates to arriving for duty about 30 minutes earlier to undertake required pre-work activities including changing into uniform, collecting and preparing equipment like guns, tasers and breathalysers, and inspecting and preparing patrol cars.
Members then need to go into briefings before starting their shifts and repeat the process in reverse at the end of them.
"The work we're talking about is genuine," Mr Gatt told reporters on Thursday.
"If they're starting at seven o'clock, you expect them, and indeed, Victoria Police requires them to be ready to respond at seven to an emergency that might occur at 7.01.
"If you think (pre-shift preparations) happen in the two minutes before they come to work, you're kidding yourself."
Victoria Police has been relying on officers working for free to meet around-the-clock demands, Mr Gatt said.
"This claim is potentially worth hundreds of millions of dollars, money that should already be sitting in the bank accounts of our hard-working members," he said.
"Our members are driven by their commitment to the safety of the community but they are workers, not philanthropists.
"Victoria Police refuses to give them back this time, so they must compensate them for it."
The union sent a letter of demand to the force on November 25 saying it had not been complying with negotiated contracts.
Victoria Police rejects any suggestion it has been underpaying officers, saying they are compensated for up to 30 minutes of work outside their ordinary hours and have been for 60 years.
"These arrangements have been reviewed at key points over those 60 years and at every stage have been retained as part of our employee terms and conditions," a spokeswoman said.
"These arrangements have long been reflected through higher salaries and allowances."
The union's claim has been raised as part of a protracted dispute being considered by the Fair Work Commission, with a decision due by year's end.
Police and protective services officers have undertaken more than a dozen stop-work demonstrations at Victorian stations and academies following a stalemate in negotiations.
The union is pushing for a 24 per cent pay rise over four years and for an end to unpaid overtime.
An agreement was reached for a nine-day fortnight and 16 per cent pay rise over four years in May but union members rejected it.
