Prime Minister Stephen Harper pledged to fight the Liberals on tax cuts during a fiery question period in which Tom Mulcair and Justin Trudeau attacked the Conservatives' newly tabled budget.

Mulcair, the NDP leader, and Trudeau, the Liberal leader, have condemned the government's plan to nearly double to $10,000 the limit for tax-free savings account contributions. They also say the government's income-splitting plan will mostly help the country's wealthiest families. Both parties seek middle-class voters in the lead-up to the 2015 election, and each argues it is the best choice to help the majority of Canadians get ahead.

Opposition MPs repeatedly questioned Harper about Finance Minister Joe Oliver's statement that any government revenue shortfall created decades from now by the tax-free savings accounts would be a matter for Harper's granddaughter to solve.

"Leave it to our grandchildren? Really? I have grandchildren, and like so many grandparents, I don't want to leave the responsibility for cleaning up the prime minister's mess to my grandchildren," Mulcair said.

Tom Mulcair presses PM on tax cuts for 'wealthiest few'1:38

Trudeau tied the tax-free savings account increase to a Conservative cut to Old Age Security. The government is gradually raising the age of eligibility to 67 from 65.

"Why is the prime minister taking $28,000 from our most vulnerable seniors to pay for his tax break for the rich?" Trudeau said.

Harper called Trudeau's assertion "completely false" and accused the Liberals of voting against other measures for seniors, which were included in omnibus budget bills containing hundreds of unrelated measures.

Stephen Harper vows to fight Liberals2:52

"One party and one party alone stands for middle-class Canadian seniors, and that's this party. And we're going to fight them every step of the way," Harper thundered across the floor of the House, the rest of his answer drowned out by cheers from Conservative MPs.

TFSA plan could cost $15B by 2080

In an interview Tuesday on CBC News Network's The Exchange with Amanda Lang, Oliver said criticism of his budget was unfounded, arguing that the benefits for Canadians today more than offset any future revenue problems that may or may not come to pass.

Stephen Harper 20150420

Prime Minister Stephen Harper responded to criticism about tax-free savings accounts by saying, 'One party and one party alone stands for middle-class Canadian seniors, and that's this party.' (Sean Kilpatrick/Canadian Press)

"I heard that by 2080 we may have a problem [due to tax-free savings accounts]

. Well, why don't we leave that to Prime Minister Stephen Harper's granddaughter to solve that problem," he said.

The Parliamentary Budget Office recently put the cost of the existing accounts at $1.3 billion this year. The government's own numbers on Tuesday said the proposed changes will reduce revenues by a further $85 million this tax year, up to a cumulative impact of more than $1.1 billion within five years.

Economist and Broadbent Institute research fellow Rhys Kesselman recently estimated that doubling the limit could cost Ottawa almost $15 billion a year within a few decades.

Harper called criticism of the accounts "a clearly preposterous argument."

"The tax-free savings accounts have been great things for Canadians, for the Canadian middle class and for the Canadian economy," he said.

"Those billions of dollars that middle-class people are putting away will create tens of billions of dollars of long-term savings in our economy, which will drive jobs and growth."

Tax-free savings account: What's in it for you?1:30