Canada's privacy commissioner is vowing to find out more about a surveillance program that collects data without a warrant on communications by Canadians.

And opposition MPs are raising questions about its legality and demanding that Defence Minister Peter MacKay explain why he approved it.

"When it comes to the metadata program, we know very little specific information at this point – but we want to find out more," Scott Hutchinson, of the Office of the Privacy Commissioner of Canada, said in an e-mail.

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Two years ago, Mr. MacKay approved the renewal of a classified surveillance program that exists in a legal grey area because it collects Canadian Internet and phone data trails – so-called metadata – as part of its efforts to look at telecommunications patterns throughout the wider world.

The question is whether this adds up to illegal spying on Canadian citizens.

"Are the Conservatives monitoring the phone and e-mail records of Canadians, yes or no?" Opposition Leader Thomas Mulcair asked Monday during Question Period.

Mr. MacKay responded to these and other questions by saying Ottawa's surveillance initiative "is specifically prohibited from looking at the information of Canadians" and that "this is foreign intelligence."

"This is something that has been happening for years," Mr. MacKay said.

On Monday, a Globe and Mail story outlined the contours of Canada's metadata-collection program, which is handled by an electronic-eavesdropping agency known as the Communications Security Establishment Canada.

Formed during the Cold War to spy on Communist states, CSEC is typically banned from any spying on Canadian citizens.

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Yet, like other spy agencies, it now draws a legal distinction between the actual conversations, which are considered privileged, and the metadata surrounding them, which are not.

As the thinking goes, phone numbers, Internet Protocol addresses, and "routing" information can be considered legal to intercept, regardless of their point of origin, as long as government technicians don't actually eavesdrop on citizens' actual conversation or read their e-mails.

The hope is that the analysis of mass-collected material can help governments zero in on networks of foreign-based adversaries. But such techniques raise obvious questions about how much domestic surveillance ought to be permitted. Documents leaked last week, for example, show that a U.S. spy agency has compelled an American phone company to cough up the "telephony metadata" of millions of American customers – daily.

It's not clear how CSEC acquires metadata. But it has been given permission from officials in Ottawa to dredge up some Canadian material.

It has been almost a decade since this spy agency – which operates under ministerial authority – first sought legal cover for its metadata-mining efforts. Liberal defence minister Bill Graham signed the first CSEC metadata directive in 2005. Mr. MacKay signed the directive authorizing a renewed program in 2011.

Parliamentarians, who are never apprised of the mechanics of electronic surveillance programs, say they want to get up to speed.

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"First of all, I'd like to see a copy of the directive that was given by the minister in 2011. That at least would clarify some things," said NDP MP Jack Harris, who put questions about the program to the minister during Question Period.

With files from Josh Wingrove