Earlier today George Osborne said he had no plans to do so -  but he refused to completely rule out the move.
The coalition government reduced the highest income tax rate from 50% to 45% in 2013.
Ed Balls, Labour's shadow chancellor, criticised Mr Osborne's refusal to rule out a further cut.
Asked on Sky News's Murnaghan programme if there were plans to cut income tax by 5% for those earning over £150,000, George Osborne said "that's not our plan".
Challenged as to whether he would explicitly rule the move out, the chancellor replied: "You can judge us by what we say we want to do. And what we want to do is increase the tax-free personal allowance to £12,500 so people full-time on the minimum wage don't have to pay income tax and millions of people are better off.
"And when it comes to higher-rate tax payers, our priority is increasing the threshold at which you pay that higher rate to £50,000.
"Those are our big tax commitments for the coming Parliament."
When asked later if he would cut the top rate of tax, Prime Minister David Cameron said: "It's not our policy.  It's not our plan.
"Our plan is to raise to £12,500 the basic rate threshold, so that we take another million people out of income tax altogether and cut tax for 30 million people. That's the plan."
But Ed Balls said: "When George Osborne cut the top rate of income tax from 50p down to 45p we know that he and David Cameron wanted to go further and actually cut it to 40p - which, if they were to do that, would mean hundreds of thousands more in tax cuts for the richest people in our society."
He added: "They need to tell us is that their plan - they won't rule it out, they should do so now."
This election issue includes income tax and national insurance levies and business taxes.
Meanwhile, Liberal Democrat minister David Laws has accused the Conservatives of "unbelievable cheek" in taking credit for personal tax allowance rises.
Mr Laws, a former chief secretary to the Treasury, said the prime minister and chancellor had failed to push for the move in talks with Lib Dems.
His party will spell out plans to "go further and faster" in increasing the allowance in the coming days, he said.
George Osborne said raising the level was one of his "big tax commitments".
The tax-free personal allowance is to rise from £10,600 in 2015-6 to £10,800 in 2016-7 and £11,000 in 2017-8.
Mr Laws told Pienaar's Politics on BBC Radio 5 live that was down to his party.
"What I can tell you is that there hasn't been a single Budget or Autumn Statement in this parliament where the prime minister or the chancellor have ever made this a Conservative ask," he said.
"The discussion they've had with Nick Clegg and Danny Alexander have always been on the basis that it's the Lib Dems pushing for this and it's the Conservatives pressing other policies which usually don't help those people on low and middle incomes."
The schools minister also told the programme his party would spell out further plans on the issue in the coming days.
"The Lib Dems left to our own devices, or putting our position in coalition talks, will want to go a lot further and faster than the measures set out in the Budget recently to help those people on low and middle incomes," he said.
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Labour is calling on the Conservative Party to vow that it won't lower the top rate of income tax if it wins the election.