Federal Attorney-General Christian Porter has rejected any link between his use of a campaign bus and the appointment of WA Liberal Party colleague Joe Francis to a lucrative tribunal position with a six-figure salary.

Key points: Mr Porter last week appointed Mr Francis to the Administrative Appeals Tribunal

Mr Porter last week appointed Mr Francis to the Administrative Appeals Tribunal He was recently head of a company which lent Mr Porter a campaign bus

He was recently head of a company which lent Mr Porter a campaign bus Mr Porter denies the bus was lent to him on a "complimentary" basis

Mr Francis was a corrections minister in the Barnett government, in which Mr Porter served as treasurer before moving to federal politics, and was one of several ex-Liberal MPs and staffers last week appointed to the Administrative Appeals Tribunal (AAT), which pays full-time members up to $244,520 per year.

Until recently, Mr Francis was the general manager of Australian Transit Group (ATG), which has provided Mr Porter and two other federal Liberal MPs with a bus for campaign use.

Attorney General Christian Porter denies the bus was lent to him on a "complimentary" basis. ( ABC News: Matt Roberts )

Mr Porter denied a newspaper report that the bus was lent to him on a "complimentary" basis.

He said the Liberal Party had reached a "commercial agreement" with ATG to pay for the three buses once the party's campaign fundraising revenues increased in the lead-up to this year's federal election.

"There was use of the bus before payment — and that's not an unusual thing because often campaign funds come in late — but the arrangement was a commercial one," Mr Porter said.

He also defended his appointment of Mr Francis, a formal naval officer, to the AAT.

"Joe Francis, in my observation, is qualified for the position," he said.

"My view is that [he] will reflect community expectations in decision making, particularly on migration issues."

Former WA Liberal MP Joe Francis has been appointed to a tribunal post. ( ABC News: Andrew O'Connor )

Porter appointing 'mates': Shorten

But Opposition Leader Bill Shorten accused Mr Porter of stacking the AAT with Liberal "mates".

"They can't help themselves, this Government," he said.

"They've never seen a mate they don't want to help and they've never seen a mate they don't want to appoint."

Opposition Leader Bill Shorten has criticised Mr Francis's appointment. ( ABC News: Nick Haggarty )

Mr Porter said it was not unusual to appoint former state and federal MPs and staffers to the tribunal.

"The Labor Party appointed Duncan Kerr, who was a former federal Labor minister, as president, to run the AAT. There's nothing wrong with that, he did a fine job," he said.

"One of the benefits of having former members of state or federal parliament is they themselves have made administrative decisions, which actually places them quite well to be able to judge when administrative decisions have been soundly made according to law," he said.

The managing director of ATG told the ABC he invoiced the Liberal Party for the three buses in January.

The ABC understands no money has yet changed hands.

Mr Francis has not responded to a request for comment.