Workers beware, is the warning from Labour - as the government looks to shake up holiday pay.

As the biggest employment law changes in a decade passed through Parliament last night, Workplace Relations Minister Michael Woodhouse said the Holidays Act is another area the government may look at.

Labour's Annette King is concerned National will push through changes that undermine workers.

She says it's "got a head of steam up" since the Employment Relations Amendment Bill passed, and with ACT, it has the numbers to pass any legislation it wants.