Bernier said he would be able to make up some of the revenue difference by getting rid of some so-called boutique tax credits — such as the deduction that can be claimed for moving expenses — should a case-by-case review find they serve no public policy purpose.

He pointed to a Fraser Institute study from last year that identified dozens of tax credits that could offset some $20 billion should they all be eliminated, but noted he did not expect the savings to be that high because there are tax credits that should stay, such as those meant to relieve the financial burden of those caring for their elderly parents.

"These are not things we want to touch," he said.

Bernier did not outright disavow the approach the Harper government took, or divulge whether he had opposed such tax credits around the cabinet table, but acknowledged his plan would take things in the opposite direction.

"I believe that this reform, it's more fair, more responsible, than other kinds of reforms," Bernier said.

Later on Thursday, his Conservative leadership rival Tony Clement took to social media to announce that he would be proposing a single tax rate, also known as a "flat tax," arguing the current progressive tax system penalizes Canadians for working harder.

Clement said he would share more details of his income tax plan later in the campaign.

The other five candidates in the Conservative leadership race are MPs Andrew Scheer, Kellie Leitch, Michael Chong, Deepak Obhrai and Brad Trost, but more are expected to throw their hats into the ring.

The Conservatives will choose their new leader May 27.

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By Joanna Smith, The Canadian Press