Deputy Prime Minister Barnaby Joyce has criticised accusations of partisanship levelled at Malcolm Turnbull over his blocking of Kevin Rudd's tilt to be United Nations Secretary General, arguing Labor gave Mr Rudd the most clear character references.

Key points: Turnbull has been accused of putting party allegiances ahead of public policy in blocking Rudd's campaign

Turnbull has been accused of putting party allegiances ahead of public policy in blocking Rudd's campaign Joyce says decision was not a "captain's pick" and Cabinet backed PM in not backing Rudd

Joyce says decision was not a "captain's pick" and Cabinet backed PM in not backing Rudd Shorten said Rudd had fallen victim to Turnbull's "petty politics"

Mr Turnbull has been accused of putting party allegiances ahead of public policy in deciding the Federal Government would not support the former Labor prime minister's campaign to be the world's top diplomat.

It has led Mr Rudd to release letters he sent to the Prime Minister over a series of months, in which Mr Rudd claims he had his former political rival's support.

Members of Federal Cabinet, including Treasurer Scott Morrison, had expressed serious concern about Mr Rudd's suitability for the job in its first post-election meeting on Thursday.

"Malcolm Turnbull's actions are pathetic, they're disappointing," Opposition Leader Bill Shorten said.

"He's not the person I thought he would be when he became Prime Minister.

"Mr Turnbull, in his first action since getting re-elected, has squibbed the chance to be a leader for all Australians, and all he's trying is to paper over the divisions in the Liberal Party.

"When his Treasurer lines up with the [former prime minister Tony] Abbott right, Mr Turnbull's no longer running the government.

"In the meantime someone, a former prime minister of Australia, a distinguished Australian, has been treated in a very shabby fashion for nothing more than I think petty politics."

Shorten 'must've had a good reason' to remove Rudd as PM

Deputy Prime Minister Barnaby Joyce said it was a difficult line for Mr Shorten to prosecute, given he was instrumental in removing Kevin Rudd as prime minister in 2010.

"He must've had a very good reason to do that," Mr Joyce told ABC News 24.

"It's possibly the same that others have as to why, in this instance [Kevin Rudd] is possibly not the best person to be head of the United Nations.

"Unfortunately we were lumbered with a compendium of events, of absolutely clear character references by the Labor party ... and it makes the job of trying to pre-select him for one of the highest jobs that we have globally — it would just be thrown back in our face.

"The invective that the Labor Party used about their own leader would be thrown back in our face."

Mr Joyce said the decision was not a "captain's pick" by the Prime Minister, and Cabinet lined up behind him in not backing Mr Rudd.

That is despite the Foreign Minister Julie Bishop and Attorney-General George Brandis speaking out in favour of the nomination during Thursday's Cabinet meeting.

"This was a decision of Cabinet," Mr Joyce said.

"When Mr Shorten decided that Mr Rudd was not the right person to be the prime minister of Australia, then I think Mr Rudd has more to answer for than anybody else."