The Labour Party will try to force the Government's hand to 'Mondayise' Anzac Day and Waitangi Day if they fall on a weekend by introducing a member's bill to make the change.

Labour leader Phil Goff announced the move this afternoon at the party's first caucus of the year - an all-day event at Auckland's Waipuna Lodge.

The bill will ensure that if Waitangi Day and Anzac Day fall on either a Saturday or Sunday in the future, the following Monday will be a public holiday. Since late last year all Australian states except Tasmania have 'Mondayised' Anzac Day.

This year, Waitangi Day is on a Sunday and Anzac Day falls on Easter Monday, which Mr Goff said deprived New Zealanders of two of their usual 11 public holidays.

He said it was now too late to make the change in time for this year, but it would ensure that next time it happened, New Zealanders would have the same benefits Australians enjoy of the extra day off.

Prime Minister John Key ruled out making any law change, saying both days should be celebrated on the date they commemorated. However, he recently said it was something that could be considered in the future.

Mr Goff said Labour had not done so in its nine years in power because its focus was on passing through four weeks' minimum annual leave.

"We did that, this is something that builds on that progress. I think New Zealanders are feeling particularly aggrieved that this year they miss out on Anzac Day and Waitangi Day. They don't get the day off to celebrate those days that they normally would."

He said people would still be able to commemorate both days on the actual date they fell without being deprived of a day off as well.

If National does not support the change, Labour would need the support of every other party in Parliament to pass it. Mr Goff said he did not believe it should be treated as a conscience vote because it was a policy issue. However, he expected to get significant support. The bill in MP Grant Robertson's name will go into the member's bill ballot when Parliament sits again in early February. It will have to be drawn from the ballot to be introduced.