Critics have attacked a move they say will nearly double the value of international travel perks for former MPs.

The calculation of how much taxpayer money former MPs are entitled to spend on international travel will change under a statute amendment bill, to be voted on next week.

Currently, the perk is calculated on the cheapest business-class return fare between Auckland and London, for the former MP and their spouse.

That would now be amended to peg the maximum rebate to the lowest Air New Zealand business-class return fare.

Advertisement

The entitlement is limited to former MPs who were in Parliament before 1999.

They can use the money to fly to any destination on any airline - the calculation determines how much can be claimed.

Legal blogger Graeme Edgeler has estimated that the change could increase the maximum rebate from $11,000 to about $20,000 a year.

Today the Taxpayers' Union called for National MP Simon Bridges' Supplementary Order Paper to be withdrawn.

"At a time when MPs are facing a public backlash for continued pay hikes, Mr Bridges wants to increase the lavish taxpayer-funded perks for retired politicians," the unions' executive director Jordan Williams said.

However, Labour's Annette King said the change had cross-party support and was simply designed to fix a mistake in the current legislation.

The fare rebate had been pegged to the lowest fare on Air New Zealand since the 1970s, Ms King said.

A mistake in wording saw that change when the long-standing entitlements were transferred to the new Members of Parliament (Remuneration and Services) Act 2013.

Advertisement

"They inadvertently left out 'Air New Zealand', which had always been the benchmark for deciding what the travel entitlement was," Ms King said.

"On July 1 every year, Parliamentary Services go online and go to Expedia I think, and they look for the lowest cost airfare, and [the rebate] stays at that for the year. It has always been benchmarked with Air New Zealand."

Because of the mistake the maximum rebate had most recently been pegged to another airlines' fare, Ms King said.

"They benchmarked it to China Air or something, which was dearer than Air New Zealand, actually. If it had been benchmarked to Air New Zealand the allowance would have been cheaper."

Ms King, who is aware of the issue after recently sitting on a former members' committee, said she wanted the change to go through, despite the backlash.

"I spoke to the Greens and New Zealand First and explained it...and they agreed that when there is an error made you should correct it.

"It wasn't to advantage or disadvantage, it was what the contract had always been."

A spokeswoman for Mr Bridges said the Supplementary Order Paper corrects a drafting error in the Members of Parliament (Remuneration and Services) Act 2013.

"If any party in Parliament votes against the amendment, it will not proceed"