The union representing 7,000 flight attendants at Air Canada is asking Federal Court to review a decision allowing fewer flight attendants on aircraft.

The Canadian Union of Public Employees (CUPE) says safety and security are at risk after a Transport Canada decision to exempt Air Canada from rules requiring one flight attendant for every 40 passenger seats.

The union says the decision is illegal because it contravenes the Aeronautics Act. It wants the ratio to remain at one attendant for every 40 passengers, rather than one for every 50, as Air Canada has been allowed.

Canadian airlines had asked for the change to cut costs on flights, saying 1 to 50 is the ratio allowed in the EU. Airlines are under competitive pressure from discount carriers.

"In any emergency situation, like an evacuation, fire, cabin decompression, a disruptive passenger or a terrorist attack, flight attendants are the first line of defence when things go wrong on an aircraft," Michel Cournoyer, president of CUPE's airline division, said in a statement.

"Reducing the number of flight attendants on board by increasing the ratio to one flight attendant for every 50 passenger seats, as Transport Canada intends, is a threat to passenger safety and security," he added.

The union wants Federal Court to review the Transport Canada decision, saying it is not in the public interest.

The safety arm of Transport Canada had conducted a risk analysis in 2002, when the proposal to change flight attendant ratios was first requested by the airline industry. It found that the 1:50 rule "on some occasions will provide less than the equivalent level of safety, while on other occasions a more than equivalent level of safety to the current 1:40 operating rule."

According to the assessment, it would be safer to operate a flight under the 1 to 50 ratio when there are fewer passengers, and less safe when the flight is at full or nearly full capacity.