Federal Opposition Leader Bill Shorten has vowed to reverse cuts to Sunday penalty rates if Labor wins the next election.

Mr Shorten made the pledge at an Australian Council of Trade Unions conference in Sydney, as workers in the retail, hospitality and fast-food sectors prepare for a reduction in their take-home pay from this weekend.

Unions have sought legal advice and are advancing their efforts to try to reverse cuts to penalty rates for Sunday workers.

An appeal to the Federal Court is on the cards from the United Voice, a union which is representing hospitality workers who face having their pay cut after a decision by the Fair Work Commission earlier this year.

How's this?

If you work on a Sunday, and get penalty rates, apparently you're "overcompensated". 

What do you think of that?