Under pressure over his energy plan, Malcolm Turnbull is promising to use a “big stick” on power companies that fail to deliver on cheaper prices.

The Prime Minister insists prices will come down through his signature NEG energy policy – a claim being openly disputed even by members of his own party.

As criticism grew over the weekend following Mr Turnbull’s about-face on legislating carbon reductions, he promised his government will set a “price expectation” confirming the most anyone should pay.

Power companies that don’t pass on savings will be put on notice by the competition watchdog and face the “toughest penalties” if they don’t turn things around, Mr Turnbull said in a video on Facebook.

“We will not hesitate to use a big stick … to make sure the big companies do the right thing by you, their customers,” he said.

Critics immediately assailed the Prime Minister’s announcement, saying there was no reason to believe his NEG scheme would lower prices in the least.

Greens Leader Richard Di Natale the modelling did not demonstrate it could bring down prices.

The Prime Minister has also stressed that his predecessor Tony Abbott once spruiked the emissions reduction target in his energy plan, the 26 per cent cut by 2030 pledged under the Paris climate agreement.

“As Tony Abbott said in 2015, it is a strong and responsible target, environmentally and economically responsible,” he said.

Mr Turnbull said under a new law, any government that wanted to change the target in the future will have to inform Australians of what impact that may have on their power bill.

The announcement comes as the Mr Turnbull moves to shore up his own job, with some MPs concerned enough to encourage Home Affairs Minister Peter Dutton stand against him.

Mr Dutton on Saturday tweeted that Mr Turnbull has his support.

In relation to media stories today, just to make very clear, the Prime Minister has my support and I support the policies of the Government. My position hasn’t changed from my comments last Thursday.

— Peter Dutton (@PeterDutton_MP) August 17, 2018

Deputy Nationals Leader Bridget McKenzie said she learnt of the changes to Mr Turnbull’s policy through his public announcement and expected to be briefed on them at a cabinet dinner on Sunday night.

Asked whether she backed Mr Turnbull, the senator said his government’s record speaks for itself.

“I think Malcolm Turnbull is our prime minister and I would like to see him stay as prime minister,” she told Sky News on Sunday.

The senator said the latest changes might make it easier to increase the emissions target in the future, a key complaint of pro-coal Coalition members. But Ms. McKenzie also noted that it would make it easier to lower emisions targets.

Richard Di Natale said his party would continue to pressure Labor not to back the plan, which he said did not do anywhere near enough to combat catastrophic climate change.

“What we’re saying to the Labor Party is – work with us,” he told ABC TV on Sunday.

“Don’t give them the tools to actually slash what is an already pathetic [emissions] target.”

-with AAP