Liberal MPs have criticised former minister Ian Macfarlane's shift to the Nationals, as talks are set on on a possible new ministry role for the coalition government partner.
Malcolm Turnbull is set to meet with Warren Truss within weeks to discuss an extra ministry position for the Nationals.
The meeting comes after former minister Ian Macfarlane announced on Thursday he was switching from the Liberals to sit in the Nationals party room.
The switch has been met with outrage from some Liberals who have accused Mr Macfarlane of blatant self-interest.
The move - if approved by Mr Macfarlane's Groom electorate council on December 12 - will take the Nationals' numbers to 22, which members say changes the ratio determining how many ministries are given to the junior coalition partner.
Mr Macfarlane first began talking to Mr Truss about the idea when he was dumped from the ministry by Mr Turnbull after the ousting of Tony Abbott in September.
Senior Nationals sources said media reports of deputy leader Barnaby Joyce's involvement in the switch were incorrect and he had no knowledge of the move until about a fortnight ago.
Victorian Liberal MP Dan Tehan said it was done for "naked ambition".
"What we shouldn't be seeing is people trying to game the system for their own self-advancement," Mr Tehan told ABC radio.
Government frontbencher Christopher Pyne described Mr Macfarlane's decision as disappointing.
Nationals senator John Williams said there was a clear agreement "the more seats you hold the more rights you have" to ministry positions.
Northern Territory Country Liberal Party MP Natasha Griggs says she was also approached to switch but declined.
"I'm very happy staying with the Liberals," she said on Friday.
Queensland Liberal National MP Scott Buchholz is also understood to have been approached, but has not commented.
Opposition Leader Bill Shorten said it was the first visible crack in the Turnbull government.
"It seems to me that Malcolm Turnbull's judgment is definitely under scrutiny because we've got the crazy situation where he promoted the wrong man, Mal Brough, and demoted the right guy, Ian Macfarlane," Mr Shorten told reporters in Melbourne on Friday.
Nationals frontbencher Darren Chester, who was in Groom on Friday with Mr Macfarlane, said his colleague had no expectations of being guaranteed any senior role in the future.
"Nothing was offered to Mr Macfarlane by the National party for him to change the party he wanted to sit with in Canberra," Mr Chester told Sky News.
Mr Chester said Mr Truss had the support of his party members until he decided to leave the job.
After that, it was reasonable to expect that part of an orderly succession Mr Joyce would step up from deputy to be leader, Mr Chester said.
A Nationals source told AAP Mr Joyce should not assume he will get the leadership, given some of his failings as a minister.
