OTTAWA -- The federal government has rebuffed Air Canada's plea to be compensated for a portion of the more than $100 million the airline says it has spent over the last five years to accommodate gun-toting sky marshals on its flights.

Newly released documents show the government dismissed the airline's concerns about costs and other aspects of the program earlier this year on the grounds that changes would "compromise public safety."

Established after the Sept. 11, 2001, attacks on the United States, the Canadian Air Carrier Protective Program involves placement of covert sky marshals, known as in-flight security officers, on select commercial routes to prevent planes from being commandeered by terrorists.

Details of the program -- including information about its scope and which flights have officers -- are a closely guarded secret.

The Canadian Press used the Access to Information Act to obtain a censored version of a secret Public Safety Canada memo prepared earlier this year for Steven Blaney, minister at the time, and an accompanying letter from a senior departmental official to Derek Vanstone, an Air Canada vice-president.

Air Canada had expressed concerns about the sky marshal program in 2013 and subsequently met representatives of the RCMP, Public Safety and Transport Canada, prompting the follow-up correspondence.

Air Canada spokesman Peter Fitzpatrick declined to comment on the documents, saying that "disclosing information about security programs or procedures could compromise their effectiveness."

However, the airline did say in a written submission to the government in February that carriers provide seats to in-flight security officers at no charge. If an officer requests a specific seat it must be provided even if it has been sold to a passenger, says the submission to a review of the Canada Transportation Act.

In these cases carriers must remove the passenger and negotiate compensation for the seat, representing "a significant cost and lost opportunities to carriers."

In the last five years the value of the seats Air Canada has provided to security officers "has reached over $100 million," the submission says. "In most jurisdictions, foreign governments provide compensation for similar programs to their carriers."

Air Canada recommended the Canadian security program buy seats from airlines at market rates. Alternatively, airlines should be allowed to write off the value of seats against taxes and to charge officers for in-flight food and entertainment

In some cases, the airline says, security officers have requested seats on so-called positioning flights, which have no passengers on board, simply to travel to another airport. Carriers should not be responsible for helping officers get to work, Air Canada says.

It recommended the RCMP share all data regarding risk assessments for individual flights with airlines, allowing carriers to make educated judgments about whether to cancel a flight, and to generally focus the program "only on flights that have a pre-agreed level of risk."

Public Safety had no immediate response to questions.

But in its letter to Vanstone, much of which remains secret, the department says the federal policy requiring airline expenditures on the sky marshal program -- including in-flight meals and luggage handling -- is "consistent with other countries" and the government is "not considering any amendments."

In addition, there is no evidence security officers are taking advantage by filing expense claims for free meals, the letter says. "The RCMP conducted a review and has confirmed that appropriate oversight and controls are in place, and that officers are not reimbursed for a meal when one is provided on board."

The air-carrier protective program contributes to the safety of Air Canada staff, passengers and equipment and, generally, all Canadians, the letter adds.

"As such, the RCMP will continue to do what is necessary aboard your aircraft, and all other Canadian airlines, to preserve the security of Canadian air travellers."