Boris Johnson has pledged to cut income tax bills for people earning more than £50,000 a year if he wins the race to succeed Theresa May as prime minister.
The former foreign secretary told the Telegraph he would use money currently set aside for a no-deal Brexit to raise the 40% tax rate threshold to £80,000.
His promise came as Work and Pensions Secretary Amber Rudd said she believed Jeremy Hunt should be prime minister.
Tory MPs have until 17:00 BST to enter the race to become party leader and PM.
Mrs May officially stepped down as the leader of the Conservative Party last week, but will remain as prime minister until her successor is chosen.
Conservative MPs who want to replace her must have the backing of eight other party colleagues to officially enter the contest.
But Michael Gove, one of 11 to have said they plan to run, has faced calls to drop out of the race after he admitted using cocaine several times more than 20 years ago.
Former party chairwoman Baroness Warsi said it would be “hypocrisy of the highest order” for Mr Gove to remain in the contest, after an article he wrote in 1999 in which he criticised “middle class professionals” who took drugs was republished.
Apologising on the Andrew Marr Show on Sunday, the environment secretary said he was “fortunate” to have avoided prison.
And at his campaign launch on Monday, Mr Gove is expected to insist he is “undaunted” by criticism, and will say he can both deliver Brexit and “stop Jeremy Corbyn ever getting the keys to Downing Street”.
Meanwhile, Mr Johnson told the Telegraph he planned to cut income tax bills for three million people, partly by using money from a pot set aside by the Treasury for a possible no-deal Brexit, and partly by increasing employee National Insurance payments in line with the new income tax threshold.
The paper estimates the move would cost £9.6bn a year.
“We should be raising thresholds of income tax so that we help the huge numbers that have been captured in the higher rate by fiscal drag,” Mr Johnson said.
Paul Johnson, from think tank the Institute For Fiscal Studies, told BBC Radio 4’s Today programme higher rate taxpayers would receive a “quite significant tax cut” under Mr Johnson’s plans – but the biggest beneficiaries would include wealthy pensioners, and people living solely off investments, as neither pay National Insurance.
Justice Secretary David Gauke, a former chief secretary to the Treasury, tweeted that Mr Johnson’s tax announcement was the “wrong priority”.
Tory MP Nicky Morgan, who chairs the Treasury Select Committee and is backing Mr Gove in the leadership contest, said: “The question for Boris is, why is this a priority when you could be obviously lifting more people out of paying income tax – the lower rate taxpayers – or you could be give people receiving child benefit an extra £15 a week?”
She added Mr Gove had been “very candid about having made a mistake and he is right to say people shouldn’t be defined by the worst mistakes they have made”.
Ms Rudd, leader of the centrist One Nation Conservative Caucus group and an influential voice on the Remain-supporting wing of the party, told BBC Radio 4’s Today that Jeremy Hunt was “the best shot we have at breaking this impasse” on Brexit.
She said anybody who says the UK is leaving by 31 October “come hell or high water” and does not have the relationships to bridge the differences in Europe “is just taking us towards a general election”.
Launching his campaign for leader on Monday, Mr Hunt will say the challenge of Brexit calls for an “experienced, serious leader”, not the “art of empty rhetoric”.
As the nominations officially open:
- Health Secretary Matt Hancock will argue he is the “fresh start” the country needs and can make the next decade the “soaring 20s”. He said he would put winning the case for capitalism at the heart of a manifesto to beat the Labour Party in a general election
- Home Secretary Sajid Javid picked up further support, with ministers Caroline Nokes and Victoria Atkins choosing to back him after Scottish Tory leader Ruth Davidson announced her support on Saturday
- Former Brexit Secretary Dominic Raab will unveil proposals to redirect £500m a year from the aid budget to create an international wildlife fund to save endangered species and habitats. “We’ve got to leave the environment in a better state than we found it,” he will say
- Mark Harper, Andrea Leadsom and Esther McVey will also launch their campaigns on Monday
- Mrs Leadsom told Today that she has the numbers to get to the first round of the leadership contest
- Sam Gyimah says as prime minister he would help young people get on the housing ladder by slashing stamp duty and creating at least a million new homes in five years
- Rory Stewart used a video message to insist he would not back down in his battle to become Conservative leader
BBC political correspondent Chris Mason said five of the candidates appeared to fall short of having eight supporters – the number required to put themselves forward in the contest.
However, he noted many Tory MPs had yet to declare who they were backing.
Whereas candidates in the past would have only needed two MPs supporting them, senior Tories decided to change the rules earlier this month in a bid to speed up the contest.