The latest parliamentary expense disclosure shows that, on average, Green Party list MPs are outspending Labour, National and New Zealand First list MPs on air travel.

The average air travel spending for non-ministerial Green Party list MPs was $9816, compared to New Zealand First's $8059, and National's $7332, and Labour's $6499.

Jordan Williams, spokesperson for right-wing lobby group the Taxpayers' Union, said the Greens "constantly say that we need to reduce air travel if we are to save the planet" and that they "need to practice what they preach".

ACT Party leader David Seymour, MP for Epsom, told Newshub: "The Green Party has always specialised in air travel and hypocrisy - in that order."

If you're unfamiliar with the term "list MP", it means the lawmaker doesn't represent an electorate, which is the case for all Green Party MPs and New Zealand First MPs.

There are two ways you can get into Parliament in New Zealand, either by winning a specific electorate, or your party can win a high enough share of the popular vote to elect individuals from its "list".

Each party has to reach a minimum threshold of 5 percent to get list members elected to Parliament, which both the Greens and New Zealand First managed at the 2017 election - but neither party won an electorate.

Looking at ministerial expenses - MPs who are also ministers, three of whom are Green MPs - New Zealand First spent the highest average amount on flights, $30,742, compared to Labour's $25,016, and the Greens' $18,883.

Shaw, who is Minister for Climate Change, defended his high international travel expenses in March 2019, explaining how the expenses are offset by planting trees.