The Greens are going into bat for hundreds of thousands of retail and hospitality workers who could face a cut in Sunday pay.
The minor party is taking the fight to retain Sunday penalty rates to Labor heartland as the opposition adopts a wait-and-see approach to a Fair Work Commission decision that may be handed down before the July 2 election.
While Labor opposes any move to reduce Sunday rates to the same level as Saturday's, leader Bill Shorten is on the record as saying he will accept the commission's decision.
Opposition industry spokesman Kim Carr is not quite as definite.
"All my experience of the Labor party is our defence of penalty rates is absolute and I would expect that to continue," he told ABC radio on Monday.
Greens MP Adam Bandt says Labor's position is everything that is wrong with the opposition.
"They talk tough on protecting weekend rates but will not do anything to protect weekend rates should they be cut," he told AAP.
Young people in particular depended on weekend rates to support themselves while studying.
They were already facing unaffordable housing, insecure work and low levels of student assistance, so cutting weekend rates would place them under immense pressure.
Mr Bandt will outline the Greens' position on penalty rates while campaigning in the inner-Sydney seat of Grayndler - held by Labor's Anthony Albanese - on Monday.
Finance Minister Mathias Cormann said the government will respect the arms-length decision of the commission.
His opposition counterpart Tony Burke said Labor supported having an independent umpire as well.
He dismissed the Greens' stance as dangerous, arguing it could open the door to a conservative government legislating to abolish penalty rates.
