Federal intelligence officials are warning their watchdogs against talking too much to each other, even as spies themselves increasingly team up on top-secret surveillance.

A 2013 letter obtained by The Globe under Access to Information laws reveals the frictions between Canada's spies and those who watch them. The correspondence shows how Canada's two spy-service watchdog agencies were last year exchanging letters about a technique used jointly by the spy agencies.

Collaboration among intelligence agencies is "the direction everything is heading in. So it's the direction we also need to go," Lindsay Jackson, a researcher at the Security Intelligence Review Committee told The Globe in an interview. SIRC is the watchdog for the Canadian Security Intelligence Service (CSIS).

Story continues below advertisement

The problem, she said, is that "there are mechanisms for the intelligence agencies to share information," but "there are no mechanisms for the review bodies to share information."

In early 2013, the watchdogs were writing to each other in hopes of drawing attention to a shared surveillance concern.

When Canadian intelligence officials learned the watchdogs were corresponding about the surveillance technique in question, they tried to find out whether the review bodies could be leaking classified information – by writing to each other.

"CSEC [Communications Security Establishment Canada] was initially concerned that the [CSEC watchdog] Commissioner may have … shared information with a third party [SIRC] that was obtained in the course of the Commissioner's classified review," reads a April, 2013, letter from CSEC's Kathy Thompson.

The spy agency's director-general of policy told her watchdog office that a review of the SIRC letters satisfied her no one violated any secrecy oaths. But in the future, "I would ask that the Commissioner's Office initiate discussions with CSEC prior to sharing additional information with SIRC," she wrote in her letter to the Commissioner.

The outreach effort between the watchdog agencies was supported in a scathing ruling last November by Justice Richard Mosley against Canada's spy agencies. The ruling occurred because the Federal Court judge read the watchdogs' public reports, where they raised red flags after comparing notes.

Judge Mosley learned the full extent of the information sharing between Canadian spy agencies and also foreign allies after reading the watchdogs' public reports. His ruling indicates he had never been told of this by Canada's intelligence agencies during five years of secret hearings. He took the extraordinary step of reopening a case he had settled in 2009. In the November ruling, he rebuked CSIS and CSEC for breaching their "duty of candour" to his court.

Story continues below advertisement

The watchdog agencies have not traditionally partnered up, given how the two spy agencies they scrutinize have traditionally pursued separate mandates.

CSEC has been collecting "foreign intelligence" for nearly 70 years. Working under the Minister of National Defence's authority, the electronic-eavesdropping agency mass-collects data and is generally banned from spying on Canadians' communications.

CSEC's watchdog – the Office of the CSE Commissioner (OCSEC) – was created in a 1996 law.

CSIS is the "human-intelligence" agency created in a 1984 law, with SIRC as its minder. More akin to police than surveillance spies, its intelligence officers have a wide latitude to collect Canadian communications – so long as they first get a judge to sign a warrant.

The legal tensions between foreign and domestic intelligence long kept CSIS and CSEC apart, save for circumstances where they were allowed to give limited investigative help to one another.

Yet post-9/11 laws, the evolving threats of terrorism and espionage, and modern surveillance methods have lately been pushing them to team up for mutual benefit in terms of collecting communications.