Michael Gove has attacked Liz Truss's tax cuts for the richest Brits as a "display of the wrong values" during the cost of living crisis.
The former cabinet minister also repeatedly declined to say whether he would vote for the measures in Parliament - but said he was "profoundly concerned".
With Tory MPs urging the PM to change course, Mr Gove said there was an "inadequate realisation at the top of government of the scale of change required".
His remarks came moments after Ms Truss refused to U-turn on the widely criticised measures, including a tax cut for those earning over £150,000.
The Prime Minister said she was "absolutely" committed to the policy while simultaneously refusing to say whether there would be public spending cuts.
But she appeared to blame communications for the fallout, admitting the government should have done a "better job" at laying the ground for the Budget.
Tory chairman Jake Berry also revealed on Sky News's Sophy Ridge programme that any MPs who voted against the measures would lose the whip.
Speaking on the BBC's Sunday with Laura Kuenssberg, Mr Gove said the PM was right to acknowledge that the events of the mini-Budget "need to be revisited, there needs to be a recognition of the mistakes".
"But it is still the case that there is an inadequate realisation at the top of government about the scale of change required," he said.
"Yes, the energy package was the most important thing in the fiscal event, but broadly 35% of the additional money that we are borrowing is not to cut energy costs, it is for unfunded tax cuts."
He added: "There are two major things that are problematic with the fiscal event. The first is the sheer risk of using borrowed money to fund tax cuts - that is not Conservative.
"The second thing is the decision to cut the 45p rate and indeed at the same time to change the law which governs how bankers are paid in the City of London.
"Ultimately at a time when people are suffering... when you have additional billions of pounds at play, to have as your principle decision, the headline tax move, cutting tax for the wealthiest, that is a display of the wrong values.
Pressed on whether he would vote for the measures, Mr Gove declined to say he would, but eventually added: "I don't believe it's right".
Another senior Tory MP, Julian Smith, also posted on social media: "The first job of an MP is to act in the interest of their constituents & in the national interest".
The former cabinet minister added: "We cannot clap for carers one month & cut tax for millionaires months later".
