Coles and Woolworths short-changed workers on overtime by setting up a payment structure “entirely foreign” to Australia’s industrial awards system, a court has been told.

A joint trial, brought by the Fair Work Ombudsman and two class action claimants against the supermarket giants, commenced in the Federal Court on Monday, alleging underpayment of workers over several years.

It came after Coles said last week it had set aside another $25 million to repay salaried managers it underpaid for years, while Woolworths has previously disclosed underpaying thousands of employees to the tune of about $390 million.

In his opening address, Fair Work Ombudsman barrister Justin Bourke KC argued the “entirely foreign” payment structure covering some workers would always “end badly for Woolworths and Coles and its employees”.

“It was like trying to put a square peg into a round hole,” Mr Bourke told the court.

He outlined to Justice Nye Perram the relevant award that capped work hours at a total of nine a day, before arguing that was not what happened in reality.

In an “extreme” example, Mr Bourke said one team manager in Sydney worked 13 hours a day, an extra four hours beyond the award limit.

Other workers did average shifts of nearly 11 hours, he said.

“That can’t be because the fridge blows up every day,” Mr Bourke said.

He said evidence would show clear standards had to be met by the companies, and that there was tacit approval of the alleged illegal conduct.

There were failures on the use of “informal” rosters, time off in lieu, and record keeping on worker overtime, penalties and allowances, he said.

“No one blew a whistle,” Mr Bourke said.

“They knew it was going on and they have to pay for it.”

He said the supermarkets should not be able “to hide behind the fact” they had very limited and ad hoc records tracking things such as time off in lieu.

“That shouldn’t be how it works,” he said.

Claims workers could have just walked out the door were “divorced from reality”, he said.

The trial, listed to run for seven weeks, continues.

– AAP