The Council of Trade Unions says Waitangi Day and Anzac Day are already budgeted for, so making the following Monday a holiday when the days fall on a weekend should not be an extra cost.
Labour Party MP David Clark says he has the political support he needs for his members' bill.
Business New Zealand chief executive Phil O'Reilly says the matter is not a priority and the debate should be about how New Zealand celebrates those two days.
Council of Trade Unions president Helen Kelly says obviously Waitangi Day and Anzac Day will still be celebrated on the day they fall - 6 February and 25 April.
However, Ms Kelly says employers budget for the days every year, so it should not make any difference if the holidays are transferred to a Monday.