Labour MP David Clark says he has the political support he needs for his members bill, which would make Monday a public holiday when either Waitangi Day or Anzac Day fall on a weekend.
The Department of Labour recommended that if the Government wanted to minimise costs to employers and the economy, it should not support the legislation.
It told the Minister of Labour that transferring Waitangi Day and Anzac Day to a Monday would cost employers $206 million or $406 million if two Monday's are taken in a year.
But Mr Clark says the department only counted the cost of paying wages for the two days every seven years when workers would not be there, but not the benefits.
"When you do those calculations you also need to take into account the benefits of having a day off, like increased productivity from rested workers, domestic tourism benefits and changes in business practice that can minimise any costs," he says.
Mr Clark says he has the support of all parties except National, giving him the votes he needs to get the bill to a select committee.