MPs will have the chance to ensure New Zealanders are not robbed of any of their hard-earned public holidays if Labour MP David Clark's Mondayisation bill comes before Parliament as expected this evening.

The Dunedin North MP is championing his Holidays (Full Recognition of Waitangi Day and ANZAC Day) Amendment Bill, which seeks to Monday-ise Waitangi Day and ANZAC Day when they fall on a weekend.

The Bill corrects an anomaly that happens roughly twice every seven years. When this glitch happens, New Zealanders miss out on the usual full complement of 11 public holidays.

"Despite outlandish criticism from National MPs, all the bill actually does is formalise in New Zealand what our neighbours across the Tasman already take for granted. When Anzac day falls on a weekend, the celebration is held on 25 April just as it is every other year, and a public holiday is observed on the Monday that follows.

"The bill is not going to impose a burden on employers and is not fiscally irresponsible," David Clark said.

"John Key's calculations on the bill read like Maths 101 gone wrong. In fact, information revealed under the OIA shows that officials, deliberately or otherwise, have focused on counting the costs of the legislative change without considering the offsetting benefits.

"Their calculations are incomplete, and it is unfortunate that the Prime Minister was reliant upon them when he made his original cautious responses to this bill.

"The costs incurred by Mondayising these de-facto national days are already accounted for by employers. There is no reason that Christmas Day, Boxing Day and January 2 should be treated any differently than ANZAC Day and Waitangi Day," David Clark said.

"Having 11 holidays guaranteed every year allows people to plan time together as a family. Employers I have spoken to value this too. They too want to be able to know with some certainty that their family members can plan to take days off that coincide with their days off.

"I look forward to bringing a full and factual debate to Parliament so that the government might see this bill for what it is - common sense and fair," David Clark said.