"If they work an hour or an hour and a half overtime, which is quite common, then they're actually working for less than the minimum wage," Hehir said.
"These are managers, people running the stores and managing other staff, and they are getting paid less than the minimum wage. Someone at KFC in the same position would be getting $24 an hour so there's a huge gap."
Hehir said Burger King had always paid its staff less than the industry average.
"They have lagged behind. We've always had to drag them kicking and screaming up to somewhere near the levels but they've always stayed behind."
Burger King is owned by The Blackstone Group, an international private equity firm.
"What we're really having to hammer out is that we think every manager should be paid the living wage of $20.55 but the pay rates are only as good as you get paid for all of those hours," he said.
Pay rates for staff on hourly wages were also low, despite negotiations for increases spanning a year, Hehir said.
The fast food operator had refused to attend meditation meetings for three weeks, he said.
"They are offering 2 cents extra an hour for maintenance crew and team trainers, they are expected to do all the other things but for 2 cents extra an hour are expected to train crew and to do all the additional maintenance work."
In a statement, Burger King marketing general manager James Woodbridge said the company had earlier in the year "taken the step to pay all employees above minimum wage".
"Burger King still remains bargaining in good faith with Unite Union and it is very disappointing that Unite Union have opted to take industrial action whilst this process is underway," Woodbridge said.
He said the company was unable to comment further.
As side from pay rates for workers "significantly" lower than those employed by Wendy's and McDonald's, Burger King also had "a lot" of health and safety issues, Hehir said.
"This has been dragging out for a year now, I don't think Burger King should be surprised that we've lost patience with them and to be honest we've only had some significant movement since we actually took the strike ballot."
Managers at McDonald's get the living wage and those employed by KFC, Pizza Hut and Starbucks earn "$23, $24, $25 an hour", Hehir said.
Unite Union has 500 Burger King members, around 40 per cent of its workforce.
