The NDP is calling for National Revenue Minister Gail Shea to defend cuts to the Canada Revenue Agency in the wake of leaked information that 450 Canadians are using tax havens.

Murray Rankin, the New Democrat critic for national revenue, says the Conservative government is cutting from the compliance section of the agency that collects taxes. Rankin says the Conservatives are failing when it comes to taking action on those who use tax havens to evade taxes.

"Independent estimates indicate that Canada could be losing between $5.3 billion and $7.8 billion annually in tax revenue as a consequence of illegal tax havens," he said.

Last week, CBC News was the only Canadian media outlet involved in revealing a massive data leak on offshore tax havens.

In what is believed to be one of the largest ever leaks of financial data, the Washington, D.C.-based International Consortium of Investigative Journalists (ICIJ) has received nearly 30 years of data entries, emails and other confidential details from 10 offshore havens around the world.

CBC News has partnered with the ICIJ over the last seven months to gain exclusive Canadian access to the information. Thirty-seven media outlets in 35 other countries are also involved.

"This leak exposes the Conservatives' failure to get serious about tax evaders that are costing Canadians billions of dollars," Rankin said.

'Real money' to be found

Last month, the federal budget included funding for measures to close tax loopholes and crack down on tax evaders.

The government proposed in the budget to give tipsters "with knowledge of major international tax non-compliance a percentage of tax collected as a result of the information provided."

The budget also laid out plans to:

Require financial institutions to report international electronic money transfers of more than $10,000 to CRA if they are already reporting those transactions to FINTRAC.

Streamline the process for getting information on third parties during audits.

Introduce new requirements for Canadians with foreign income or properties to report more information and extend the amount of time the CRA has to reassess them.

Canada isn't measuring its tax gap, Rankin says, but allies like Australia, Britain and America prepare estimates of how much tax money they are losing out on.

Rankin says he fears the government will go after easier targets, when one report has pegged the worldwide value of money in offshore accounts at $20 trillion.

"My fear is that the government will go after the low-hanging fruit, by which I mean somebody who's clearly evading taxes, simple, they've got him. What about the intricate corporations, international trusts, foundations that together avoid hundreds of millions of dollars? That, it'll take longer. That is more difficult, but that may be where the real money is and that's what the British are going after now aggressively."