Australian unions have vowed to fight the business lobby's push to cut weekend penalty rates, warning the move could create a US-style underclass.

John Osborn, the chief operating officer for the Australian Chamber of Commerce and Industry, said it was mobilising members for a national campaign to cut weekend penalty rates.

"Tony Abbott ... if you want a fight over weekends in the Australian community, let's do that": ACTU Secretary Dave Oliver. Credit:Janie Barrett

''We need to look at Sunday penalty rates and how they are adversely affecting employment opportunities, particularly for the young,'' he said.

''We should bring Sunday penalty rates down at least in line with Saturday rates. We don't live in the 1950s any more, we live in a modern 24/7 community in the digital age and we need workplace laws that reflect that.''