Air Canada has declared its aircraft no-fly zones for pets.

As of next month, animals will no longer be allowed aboard any Air Canada flights.

Darren Jakubec's pet dog died of carbon monoxide poisoning while travelling in an Air Canada cargo hold.

While the airline barred pets from aircraft cabins last September, the restriction now applies to the baggage compartment as well.

In a letter sent to the Canadian Transportation Agency on Wednesday, the national carrier said, "please be advised that Air Canada will cease the carriage of pets as checked luggage on domestic as well as international routes [including transborder routes], as of July 15, 2007."

Air Canada said the decision was prompted by "record load factors" for the past three years, as well as new security requirements that are leading passengers to check more luggage.

"It really comes down to a question of carrying bags for the vast majority of our customers or carrying pets for a small number of our customers," spokesman Peter Fitzpatrick told CBC News.

He denied the ban was related to a case in January 2004 when a B.C. family's pet dog died of carbon monoxide poisoning while travelling in an Air Canada cargo hold.

Although Air Canada said it was not responsible for the accident, owner Darren Jakubec argued that the rules around liability were unclear. He took his case to the CTA, which agreed, but concluded that airlines were not responsible for the health of pets.

"The Canadian Transportation Agency did exonerate Air Canada in that case, although they did ask us to clarify our rule," Fitzpatrick said. "This is really about improving customer service."

Fitzpatrick said the airline will allow people with existing reservations to fly with their pets after the deadline. Otherwise, animals will be permitted to travel only on more expensive Air Canada cargo flights that have trained animal handlers.

Air Canada's website still advises passengers that pets are permitted in the cargo compartment.

Hedy Hope, a spokeswoman for the Calgary Humane Society, said it's not fair that pet owners will have to resort to cargo flights.

"I think it's important that if people object to not having their pets able to travel with them on the plane that they should file a complaint to the company and state their objections," Hope told CBC News.