The leaders of both major parties say they want their caucuses to release details of members' use of the MPs' international travel perk after the decision by Speaker Lockwood Smith to withhold the information.

Yesterday, John Key (National) and Phil Goff (Labour) said they would ask their caucuses to consider releasing their spending on the international travel rebates, which range from 25 per cent for second-term MPs to 90 per cent for others who have served more than four terms.

Both also believed Dr Smith was wrong to decide not to include the rebate spending in the quarterly release of MPs' travel and accommodation costs.

Act leader Rodney Hide also said he believed the Speaker's decision was wrong, despite getting caught out using the perk himself when details of MPs' expenses were made public.

Mr Key said he believed the National caucus should voluntarily release the information and he would raise it at the next meeting.

"Once the genie is out the bottle, it's out. My view is withholding the information won't achieve anything."

Mr Goff said he would talk to his caucus about releasing the details.

"My personal view is that there needs to be transparency around the use of the travel privileges or there is a risk they are abused."

Mr Key did not believe Dr Smith had taken the right approach in claiming travel constituted private spending because the perks were effectively paid for by MPs forfeiting part of their salary.

The PM said Dr Smith was "academically correct. But in the end we're dealing with the world of politics and I've advocated for transparency."

Mr Goff also added his voice to that of the Green Party and Act in seeking a wider review of the perk, which he said had to be changed. He said it was up to the Prime Minister to do that.

He believed subsidies were appropriate where the travel was related to an MP's work. But he did not support retaining the perk for holidays by politicians. He also believed limits were needed on its use rather than leaving it to the MPs to use at will.

"If this is paid for, as the Speaker says, out of all MPs' salaries, then the reward can't be disproportionately enjoyed by some at the expense of others," Mr Goff said.

Although MPs' salaries are set by the independent Remuneration Authority, their "perks" are decided on by the Speaker on the advice of the closed-door Parliamentary Service Commission - a grouping of MPs from each party.

The authority takes the perks' value into consideration when it sets MPs' base salary rates.

The Speaker will now release only the total spending on the rebates in each quarter alongside the amount the authority valued the perk at.

He made the change after a dramatic cut in the use of the rebate last year by MPs.

The authority had estimated the total value at $1.176 million but spending was $433,000. The reduction followed the start of regular releases of spending and revelations such as Mr Hide taking his partner, Louise Crome, to Europe and to Hawaii.

Dr Smith said MPs had already paid for the travel because the authority left about $9650 off the base salary to take account of the perk.

Personal benefit

What the Remuneration Authority regards as a personal benefit rather than work-related when setting base salary for MPs:

* Superannuation: $26,200.

* 5 per cent of MPs' domestic travel: $1176.

* 45 per cent of spouses' domestic travel: $3449.

* 100 per cent of MPs'/spouses' international travel: $9646.