A sign for the Government of Canada's Communications Security Establishment (CSE) is seen outside their headquarters in the east end of Ottawa on July 23, 2015. Close allies will curb or even halt the flow of intelligence to the Communications Security Establishment if the electronic spy agency is forced to spill its closely guarded secrets in open court, argues a senior CSE official.In turn, that could dry up the flow of "quality information necessary to ensure the safety and protection of Canadians and Canadian interests," says Scott Millar, director general of strategic policy and planning at CSE. THE CANADIAN PRESS/Sean Kilpatrick

OTTAWA - Close allies will curb or even halt the flow of intelligence to the Communications Security Establishment if the electronic spy agency is forced to spill its closely guarded secrets in open court, argues a senior CSE official.

In turn, that could dry up the flow of "quality information necessary to ensure the safety and protection of Canadians and Canadian interests," says Scott Millar, director general of strategic policy and planning at CSE.

Millar's warning comes in an affidavit filed in a legal tug-of-war between the federal government and a civil liberties watchdog over what CSE must disclose in court.

The British Columbia Civil Liberties Association is suing the national surveillance agency, claiming it breaches the constitutional rights of Canadians by intercepting their private communications.

The organization filed the lawsuit almost three years ago in the Supreme Court of British Columbia. But an initial phase of the legal saga played out this week in Federal Court in Ottawa with cross-examination of witnesses over disclosure of federal records in the broader case.

The Ottawa-based CSE uses highly advanced technology to intercept, sort and analyze foreign communications for morsels of intelligence interest to the federal government. It is a member of the Five Eyes intelligence alliance that also includes the United States, Britain, Australia and New Zealand.

A federal watchdog declared earlier this year that the spy agency broke privacy laws by sharing information about Canadians with foreign partners.

Certain types of metadata containing Canadian identity information were not being properly "minimized" — stripped of potentially revealing details — before being shared with the CSE's four key foreign partners.

Metadata is information associated with a communication — such as a telephone number or email address — but not the message itself. Still, privacy advocates argue it can be highly revealing.

CSE's activities are shrouded in secrecy, says Grace Pastine, the civil liberties association's litigation director.

"CSE is required to have policies in place to protect the privacy of Canadians, but it has not provided the details of those policies to Canadians," she said in a statement. "We're calling on the federal government to state clearly who it is watching, what is being collected, what is being shared with foreign governments and how it is handling Canadians' private communications and information."

In his affidavit, Millar says if CSE is forced to reveal sensitive material provided to it by a Five Eyes agency, or related to the alliance's processes, it is very likely to be damaging.

"A loss of faith in either the commitment or ability of CSE and the Government of Canada to protect such information could result in a significant decrease in information being shared with CSE and even a termination of access," he says.

"Damaging trust and respect through disclosure of information against the expressed wishes of one or more of our Five Eyes partners would have a detrimental effect on future collaborative efforts, consequently harming not only the interests of Canada, but also those of our closest partners."

The federal Liberals have expressed concerns about CSE, committing during the election campaign to limit the agency's power by requiring a warrant to engage in the surveillance of Canadians, the civil liberties association noted.

However, to date, the government continues to oppose the lawsuit.

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News from © The Canadian Press, 2016