Labor will overrule the independent workplace umpire and legislate to fully restore Sunday penalty rates if it wins the next election.

Opposition Leader Bill Shorten made the promise in a speech to the Australian Council of Trade Unions on Tuesday, as workers across four industries prepare for the pay cuts that begin rolling out this weekend.

"My team and I have stood with you to fight this cut in the Parliament and the community – and I know you're still fighting it in the courts," Mr Shorten said.

"Tonight I give you this solemn pledge for the fight beyond 1 July.