A politically explosive decision on the future of penalty rates now appears highly unlikely to be announced during the federal election campaign.

Employer groups want Sunday loadings cut to Saturday levels for hundreds of thousands of hospitality, retail and entertainment workers.

Federal Labor and unions strongly oppose such a move.

It was thought the independent Fair Work Commission (FWC) could hand down its decision before an expected double dissolution poll on July 2.

But the FWC has agreed to take more evidence until June 3 from employers and unions.

It is understood the commission could also accept submissions after June 3.

The commission will then privately reach a decision, which its own benchmarks say should then be announced within 12 weeks, severely cutting the chances of a mid-campaign ruling.

The Federal Government's official position is penalty rates are a matter for the FWC.

But a number of Government members support a Productivity Commission report that recommends reducing Sunday penalties to Saturday levels across the sectors.

For workers under the General Retail Industry Award, for example, double time on a Sunday would fall to 125 per cent of weekday pay for full-time or part-time workers.

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