Canada's secretive electronic-eavesdropping agency is being pulled into court to face allegations that it is illegally seizing citizens' telecommunications, in what observers describe as a groundbreaking lawsuit.

The British Columbia Civil Liberties Association announced Tuesday that it is suing the government, asking a judge to stop certain surveillance activities of the Communications Security Establishment Canada for allegedly violating the Constitution.

"To our knowledge this is the first challenge to CSEC's operations in Canada," said Caily DiPuma, counsel for the BCCLA. She added that "the ultimate goal would be to force Parliament to change the law."

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Asked about the suit, CSEC spokeswoman Lauri Sullivan e-mailed The Globe to say that "under the law, this organization is prohibited from targeting Canadians."

The BCCLA suit is being supported by OpenMedia.ca, an activist group for Canadian Internet users. The two groups held a joint news conference in Vancouver on Tuesday. "There is no question that recent revelations … have sparked a global debate," said Ms. DiPuma. "It has been in the media. The world is asking questions of these governments and the time is now."

In the United States, the National Security Agency is under fire after a series of leaked documents exposed just how much information the NSA has been collecting on Americans' telecommunications.

The NSA's Canadian counterpart, CSEC, found itself at the centre of a controversy in Brazil this month, after a leaked document showed it had been spying on that country's Ministry of Mines and Energy. In June, The Globe and Mail unearthed records showing that CSEC has been collecting some Canadian "metadata" – telephone and Internet traffic records – in the course of scouring global telecommunications trails for investigative leads.

In Canada and the United States, laws typically require federal agents to get warrants before they intercept any telecommunications. Federal agents who would do otherwise risk criminal conviction for illegal search and seizure.

But whether such laws ought to apply to electronic-eavesdropping agencies that "mass collect" data, including at least some citizens' telecommunications traffic, is a crucial question. While the NSA and CSEC typically blunt criticisms by saying they aim their ears outward for "foreign intelligence," the fallout from the Sept. 11, 2001, terrorist attacks has also drawn them into closer partnerships with domestic police and intelligence agencies.

Legal battles were foreseen years ago. In the 2001 Anti-Terrorism Act, Canada's Parliament passed a law stating CSEC could be shielded from illegal search and seizure laws in the Criminal Code, provided that the Minister of National Defence sign off on "authorizations" allowing such surveillance.

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In an 11-page filing to the Supreme Court of British Columbia, the BCCLA says that nearly 60 ministerial authorizations for CSEC have been signed or renewed since 2002. The suit alleges that this system runs afoul of the Charter of Rights and Freedoms, which states that "everyone has the right to be free against unreasonable search and seizure."

"They can try to immunize themselves from criminal liability but they can't immunize themselves from constitutional liability," said Ms. DiPuma, the BCCLA counsel.

Legal observers find the lawsuit intriguing, saying that the constitutional argument may prove a strong one, even if very little is known about how CSEC does its work.

Government lawyers will almost certainly try to move proceedings behind closed doors, said Paul Cavalluzzo, a lawyer who this month argued a closed national-security case where eight Supreme Court judges sat in an undisclosed location.

"There haven't been many national security cases that have come before the courts," said Peter Hogg, an expert in constitutional law. "… It's going to be a seminal case."