The Canadian Transportation Agency has ordered Air Canada and Porter Airlines to alter their compensation policies to protect passengers who are unable to fly to their destinations as planned.

The regulator says Air Canada, the country's largest carrier, must pay passengers between $200 and $800 cash, or three times that in travel vouchers, if they are involuntarily bumped from flights.

The Montreal-based airline has the flexibility to switch to smaller aircraft for operational and safety reasons, but the agency says Air Canada must pay compensation if it can't prove that it took all reasonable steps to avoid the substitution.

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In a separate decision issued Thursday, the agency ordered Porter to refund fares paid for cancelled domestic flights and provide compensation for reasonable expenses when flights are delayed. It called the Toronto-based airline's current policies unclear, and said Porter should make "reasonable" efforts to inform passengers of schedule changes and the reasons for them.

Air Canada has until Sept. 18 to comply, while Porter was given until Sept. 30 to revise its tariff provisions.

Both rulings stemmed from complaints filed by consumer rights activist Gabor Lukacs, who called the rulings victories for passenger rights against the Canadian airlines.