Former party chairman Sir Jake Berry added his name on Sunday to the Tory MPs backing rival legislation trying to force a U-turn from the Prime Minister.
Mr Sunak is also facing a split in opinion from within his own Cabinet, with Levelling-Up Secretary Michael Gove understood to be backing an end to the moratorium.
Transport Secretary Mark Harper acknowledged the situation is “not easy” but insisted the stream of Tory MPs saying they will not contest the next election is nothing for the party to worry about.
Former prime ministers Ms Truss and Mr Johnson are among more than 20 Conservatives backing a pro-wind amendment to the Levelling Up Bill.
Alok Sharma, who was the president of the Cop26 climate summit, has also backed the legislative move from former levelling-up secretary Simon Clarke.
Elliot Colburn and former ministers Robert Courts and Kevin Foster will also add their signatures to the amendment, the PA news agency has been told.
Along with private backers, a rebel source said 30 Tories back the bid, coming close to eroding Mr Sunak’s working majority of 69 votes if other opposition groups join Labour in backing the amendment.
Sir Jake said Mr Gove’s divergent opinion “spells real danger for my Government”, suggesting it is a “first crack in the wall” of discipline for Mr Sunak.
“Boris Johnson famously used to call wind turbines the white satanic mills of the North of England when they were building them all over my constituency,” he told the BBC’s Sunday with Laura Kuenssberg programme.
“He’s changed his mind on them; I to a large extent have changed my mind, and I’m going to be supporting Simon Clarke.”
The former minister, who was awarded a knighthood by Mr Johnson, argued that soaring energy bills are the key reason to invest more in renewables.
Mr Johnson did not seek to overturn the effective moratorium on new onshore wind projects, in place since 2015, during his time in Number 10.
Mr Sunak is seeing a steady stream of Conservative MPs, many of whom are relatively young and were thought to have bright careers ahead, announce their exit plans.
His net-zero tsar, Chris Skidmore, became the ninth to say they will not contest the next election, following levelling-up minister Dehenna Davison.
Mr Harper insisted they are setting out their positions now because Tories have been given until December 5 to make a decision due to the review into constituency boundaries.
He told Sky’s Sophy Ridge on Sunday: “You are going to see those all bunched together so I don’t think there’s anything particularly to write home about that.”
On dire polling the Tories are struggling to bounce back from, he said: “If we are being realistic about it, we are not going to turn things around overnight.”
Mr Harper told the BBC “I accept things are not easy at the moment” but said Mr Gove will be talking to colleagues about the planning policy and will be considering changes.
Labour is planning to back the Clarke amendment to pile the pressure on Mr Sunak, even though the party believes it “swaps the ban for what is still a highly restrictive planning regime on onshore wind”.
Shadow climate change secretary Ed Miliband said: “Onshore wind is the cheapest, cleanest energy we have. The Tories’ ban has kept bills high and damaged our energy security. Rishi Sunak‘s weakness means he’s having to be dragged to scrap it by his backbenches. He should swallow his pride and U-turn now.”
The Prime Minister is not only facing a challenge over onshore wind, but on building targets as well.
He was forced to pull a vote on the legislation that would set a target of building 300,000 homes per year when around 50 Tory MPs threatened to rebel.