Undercover Mounties have been carrying loaded guns on Canadian commercial flights since 2001 after being granted a secret exemption from air safety rules, but the practice will be formally permitted in a rule change this month.

A change published Wednesday to the Canadian Aviation Security Regulations shows the Conservative government will allow "Canadian in-flight security officers" to carry loaded guns on board in the course of their duties, beginning later this month.

RCMP began putting undercover officers on planes after the terror attacks of Sept. 11, 2001, but Canadian regulations have until now specifically banned airlines from allowing loaded guns on flights. The RCMP program was at odds with the published rules.

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After the change was published on a government website Wednesday, Transport Canada and the office of Minister Lisa Raitt referred questions to the RCMP. On Thursday, however, after a Globe and Mail story was published online, Ms. Raitt's spokesperson said armed Mounties have been permitted on commercial flights for years under a special exemption.

"In-flight security officers have been permitted to carry loaded firearms, when they are acting in the course of their duties, on flights since the Canadian Air Carrier Protective Program [CACPP] was created post 9/11," Ms. Raitt's press secretary, Jana Regimbal, said in an e-mail statement Thursday.

While the rules specifically barred this, the statement said RCMP had been using a "regulatory exemption" in the Aeronautics Act, which allows the minister to exempt people from rules if doing so "is in the public interest." Such exemptions are not published. This month's regulatory change, which takes effect July 14, "codifies the exemption into regulation," the statement said.

Asked about the armed-officer program, WestJet spokesman Robert Palmer said safety and security are the airline's top priorities. "To that end, we actively support and participate in the Canadian Air Carrier Protective Program, established following the terror attacks in the United States on September 11, 2001," he said in an e-mail, adding "it would be potentially detrimental to public safety" to share details of the program.

NDP public safety critic Randall Garrison said Thursday the move is at odds with the government's recent push to reduce the number of flight attendants required – from one per 40 passengers, to one per 50 – a move Ms. Raitt has said is in line with international standards.

"If we're concerned about security and safety on airlines, we should be equally concerned for the number of flight attendants," said Mr. Garrison, whose party has opposed the flight attendant changes. "… We're all concerned about air safety. I'd like to see some consistency across the board."

The RCMP on Wednesday said the rules make it clear their officers can carry a loaded gun in the course of their duties, but declined on Thursday to say whether that was already happening, before Ms. Raitt's office acknowledged it was.