Finance Minister Mathias Cormann was just doing his job when he booked flights costing $37,000 to meet with crossbenchers last year, his cabinet colleague Dan Tehan says.
Senator Cormann met with the crossbenchers in Adelaide on June 22, as part of a campaign to pass big business tax cuts, before flying home to Perth.
The flights, which began in Canberra, were on a defence jet as no commercial flights were available to facilitate the journey, an ABC report revealed on Friday.
A spokeswoman for the minister told AAP the booking was "approved in the appropriate way" and that he conducted official business in Adelaide on his way home to Perth from Canberra.
The flights came the day after federal parliament approved the government's personal tax cuts and as the coalition was trying to rally Senate support for proposed tax cuts for big businesses.
The government has since shelved the corporate tax relief package.
Greens senator Sarah Hanson-Young isn't sure the spending "would pass the pub test".
"$40,000 sounds like a lot of money for a meeting that he was obviously very desperate to do but didn't result in very much," she told ABC Radio National on Friday.
But Mr Tehan said Senator Cormann had been "hellbent" on getting tax cuts over the line and made the trip to Adelaide to negotiate with crossbenchers.
The education minister said Australian taxpayers would be "very pleased" to know their finance minister was trying to ensure they pay less tax.
"The Australian taxpayer can have full confidence in the finance minister, that everything he seeks to do is about them paying less tax," he told reporters in Melbourne on Friday.
"We've got to be able to do our job...what the finance minister was doing, was doing his job."
Shadow treasurer Chris Bowen said the vast majority of VIP flights by governments of both stripes adhered to the appropriately strict rules.
But he restrained from criticising Senator Cormann's trip.
"We are unaware of the circumstances. It's up to minister Cormann to outline why this was appropriate," Mr Bowen told reporters in Nowra.
Senator Cormann flew back to Canberra from Perth for another parliamentary sitting week on June 24 at a cost of $1,808.02.