Another backbench revolt against the Prime Minister is brewing over his plans to deliver a keynote address to this weekend's Australian Republican Movement dinner.

Key points: Liberal backbencher warns PM could damage the Government by advocating for a republic

Liberal backbencher warns PM could damage the Government by advocating for a republic Turnbull co-founded Australian Republican Movement, fought bitter battle with Tony Abbott before 1999 referendum

Turnbull co-founded Australian Republican Movement, fought bitter battle with Tony Abbott before 1999 referendum Labor ARM member Matt Thistlethwaite says dinner will be test of Mr Turnbull's political courage

"This just pisses off our base," one Liberal backbencher told PM, adding it could lead to a decline in Liberal Party membership.

"Pauline Hanson and the National Party and people like that will be rubbing their hands with glee."

He also said any attempt by Mr Turnbull to advance the republican cause could do the Government political damage.

"When you look at our position in the polls you would think that would put a stop to an issue like this," he said, comparing the Prime Minister to former Labor PM Paul Keating.

"Each time he got in strife you'd see him starting talking about anything to do with a republic."

Another pro-monarchist coalition backbencher, Craig Kelly, said he was waiting to hear what Mr Turnbull had to say at the dinner.

"He may very well say the republican cause in Australia is a lost cause," he told PM.

"We're always watching what our Prime Minister says and the great thing about our side of politics is if we disagree with what our prime minister or minister says, as backbenchers, we are more than free to voice that dissent."

Mr Turnbull has for decades been one of the country's strongest advocates for an Australian head of state.

As a one-time leader of the Australian Republican Movement in the lead-up to the failed 1999 referendum, he fought a bitter public battle against monarchist spokesman Tony Abbott, who he last year later toppled as prime minister.

A spokesman for Mr Abbott told PM: "Mr Abbott's position on the republic is clear", before declining further comment.

Speech a test of political courage

Opposition Leader Bill Shorten is a supporter of the republic and has vowed to begin moves toward another referendum, if he wins the next election.

Labor frontbencher Matt Thistlethwaite is a long-term member of the Australian Republican Movement and says Mr Turnbull's speech on Saturday is a test of his political courage.

"Is he going to stand up for what we all know what he believes in, which is an Australian head of state?" he told PM.

"Or is he going to be a coward and succumb to conservative pressure and either pull out of the event or even worse go along and tell republicans that the time is not right for an Australian head of state?"

The dinner celebrates the 25th anniversary of the Australian Republican Movement, which Mr Turnbull helped found.

Current ARM chairman Peter Fitzsimons said he was "absolutely thrilled" to have the Prime Minister attend the event.

It is understood he accepted the invitation two weeks ago.