SDA state secretary Peter O'Keeffe told Hutchinson's program the proposal was "unacceptable".
"Obviously this manager has decided for reasons of his own to request people to come and work unpaid," he said.
"As soon as he put that notice on the notice board SDA members started ringing us and we immediately got in contact with the manager and told him this was unacceptable and it would not be allowed.
"He argued perhaps a little bit but then took the message down. We also raised it with Coles head office, because this is clearly very concerning. Coles at the senior level are aghast that he actually took this step and they have taken steps to make sure not only that it doesn't proceed but that it doesn't happen again."
O'Keeffe agreed with Hutchison when he suggested it was a "one-off".
"He (the manager) tried to protest that it was an acceptable practice, we made it very clear that it wasn't and he didn't put up too much of a fight," O'Keeffe said.
"If an employee of Coles works for the benefit of Coles or indeed for any other company they then are both entitled and required to be paid for it."
Massive pressure
However in a letter to the radio show an employee of Coles, named only as 'Nick', said the proposal was emblematic of the pressure on workers at the supermarket giant.
"It's weird (but) the manager involved sounds like he cares about the business," Nick was quoted by Hutchinson.
"I can't imagine he was going to get any financial benefit out of it. It is not right but I wouldn't be too harsh on that person.
"I have been a night employee at Coles for four years. The motive for this manager would have come from pressure from the regional manager to have the work completed within a certain time frame.
"Hours have been cut drastically at each stores, workloads increased massively.
"Having said that the pressure from above does not result in an increase in hours to be passed on to the store to complete the work. The manager would have been pressured and may have felt this was the only measure to ask his staff for this free work.
"The overhaul of work within stores also happens frequently when the big managers from quote 'over east' are planning a visit.
"If only they did unannounced visits they would realise how badly managed each store is
"So in short, it does come from above.
"Coles head office just would not have approved an increase in budget for this work to get done."
Coles issued a statement to ABC in response to the story.
"Coles values the hard work of all of our team members and the notice in the store is completely out of step with Coles' way of working," the statement read.
"The notice, which was posted by a trainee manger, was quickly removed. Any team members working at the stated time will be paid as normal."
However "an insider" quoted by Hutchinson said unpaid work was a common practice at Coles.
"It is good to see the appalling condions of Coles finally being seen from the outside, unpaid work is rife," Hutchinson quoted the insider as saying.
"Hours and wages keep getting cut and more is expected to be done with less.
"Everyone is overworked. This store manager would have been under extreme pressure from a regional manager and state operations manger to get the job done without spending any more money."
