Squabbles and insults are flying between Coalition MPs with former prime minister Tony Abbott posting on social media that frontbencher Scott Morrison "should have the gumption to think for himself".

Key points: Tony Abbott took to social media to level more insults at Treasurer Scott Morrison

Tony Abbott took to social media to level more insults at Treasurer Scott Morrison Mr Abbott's migration suggestion was slapped down by the Treasurer and Trade Minister Steve Ciobo

Mr Abbott's migration suggestion was slapped down by the Treasurer and Trade Minister Steve Ciobo Meanwhile, Nationals are still bickering about leadership, with Andrew Broad the latest to take a swipe

Mr Abbott posted on Facebook and Twitter today to continue his argument with Mr Morrison about Australia's immigration level.

The Treasurer rejected Mr Abbott's call to cut the immigration rate, saying it would cost the economy billions of dollars.

Mr Abbott accused Mr Morrison yesterday of being captured by Treasury, which he said was always in favour of more immigration.

The former PM took that a step further today, saying on Facebook:

"If Treasury is right, why not solve the deficit simply by ramping up immigration?

"We should not let Treasury's accounting rules stop the Government from acting in our medium-term national interests and Scott should have the gumption to think for himself."

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Trade Minister Steve Ciobo has also strongly disputed Mr Abbott's call for a cut in the immigration level.

Mr Ciobo told RN he could not disagree more strongly with Mr Abbott's comments.

"I think it's a great shame that we see immigration, and in particular, immigrants, having the finger of blame pointed at them on issues like house prices and depressed wage growth," he said.

"I think that's lazy, I think it's highly inaccurate."

The spat has happened while Prime Minister Malcolm Turnbull is in the United States for talks with President Donald Trump, and comes as leadership problems continue to hit the junior Coalition party.

Nationals leader Barnaby Joyce is on personal leave, but has given a high profile interview from the apartment he is living in rent-free with his new partner.

Today, one of his own team took a big swipe at Mr Joyce.

Nationals backbencher Andrew Broad quoted the late evangelist Billy Graham saying "when character is lost, all is lost", suggesting it was applicable to the leadership of his party.

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He also said he would tell a meeting of Nationals members next week that Mr Joyce should resign as Deputy Prime Minister to "spend some time on the backbench".

This makes him the first federal Nationals MP to publicly say Mr Joyce should step down.

The fact Mr Joyce was not acting Prime Minister in Mr Turnbull's absence influenced Mr Broad's decision.

"I need to know as a Member of Parliament that the person who is going to be the acting prime minister has got their mind on the job," he said.

Senior Liberals have not endorsed Mr Joyce's leadership, instead repeating that it is a matter for the Nationals to decide.

About eight of the 21 members of the Nationals partyroom are understood to want Mr Joyce to quit the leadership, while another eight support him staying.

The rest are understood to be undecided and checking the views of their constituents.