"After today, we're not moving any further, we can't afford to," one senior figure said.

Opposition Leader Bill Shorten's position on penalty rates dominated the campaign trail on Monday after the Greens tried to wedge Labor on workplace relations by challenging the ALP to support legislation to lock in current levels of penalty rates.

He also came under pressure from unions after The Australian Financial Review revealed on Monday the ACTU was pushing Labor to take more action to protect the take home pay of workers if penalty rates were cut by the Fair Work Commission.

If it wins power, Labor has promised to intervene in the commission proceedings to argue in support of current levels of penalty rates, but it has also said it would abide by the commission decision.

Mr Shorten, who appeared in television advertisements on Sunday promising to ''keep'' weekend penalty rates, said on Monday he could guarantee to workers ''that only a Labor government can be trusted to protect our penalty rates system''.

''I do also just caution the Greens, from their side-show position, that they need to be careful ... they're playing with fire by proposing that a government should be able to legislate on specific penalty rate outcomes,'' he said.

''They are loading the gun for future conservative governments to pull the trigger, because what the government has the power to put in, a future government has the power to dismantle. The independent umpire, the system of conciliation and arbitration, has served this nation well for 120 years.''

The Australian Manufacturing Workers' Union said on Monday it did 'not support the Green's proposal to introduce legislation to Parliament that would take away the decisions about penalty rates from the Fair Work Commission".


"This proposition may be clever politics in an election context, but any experience in industrial relations shows that legislating these rights puts them at more, not less, risk," the union's national secretary Paul Bastian said.

"We are disappointed that the Greens Party have decided to play politics with this issue."

"The evidence speaks for itself. Millions of workers rely on penalty rates to earn a decent standard of living and an objective and evidence based approach to this issue will continue to show that."

"In the event that the Fair Work Commission, or a future Turnbull Government removed penalty rates, the AMWU would not rule out any action to protect living standards, including legislative, legal and industrial action'

Opposition workplace relations spokesman Brendan O''Connor said on Monday Labor would not back enshrining current penalty rate levels in legislation

"If we were to go down the sort of reckless path of the Greens in an attempt to legislate, you would be providing the mechanism for the Liberals to abolish penalty rates by legislation," Mr O'Connor said.

Opposition finance spokesman Tony Burke claimed the Coalition had made a submission to the Fair Work Commission ''in which it is encouraging them to get rid of penalty rates''.

But the Coalition has not made such a submission. It appears he was referring to employers submitting recommendations by the Productivity Commission inquiry to cut Sunday penalty rates to lesser rates than apply on Saturday.


Labor has continually claimed the Coalition set up the inquiry with the objective of reducing penalty rates.

''Be in no doubt of the dangerous risk that is posed by the Greens policy on this one,'' Mr Burke said.

''Be in no doubt about it. Once you open the door that you won't have the umpire make these decisions, and you open the door that these decisions will be made through legislation in the Parliament, at that point, you've given free range for a conservative government to do the exact opposite.''

Employment Minister Michaelia Cash said: "Labor either believes in and supports the independence of the Fair Work Commission or it doesn't."