MONTREAL -- The future of Bombardier's sole Canadian CSeries order is in serious doubt after Ottawa confirmed it would not allow passenger jets to fly out of Billy Bishop Toronto City Airport.

Transport Minister Marc Garneau tweeted Thursday night that the government will not reopen an agreement with the City of Toronto and Ports Toronto that would need to be renegotiated to extend the runway at the island airport and permit jets.

Bombardier, which didn't immediately respond to requests for comment Friday, has a lot riding on its CSeries contract with Porter Airlines.

In 2013, Porter placed an order worth US$870 million for a dozen of the 110- to 125-seat CSeries aircraft on the condition that they would be allowed to fly at the airport. It also has options for 18 more aircraft that would raise the list price to US$2.15 billion if all options are exercised.

Porter Airlines declined comment. It had hoped to use the CSeries plane to fly to destinations across North America that were beyond the reach of its fleet of Q400s.

If Porter walks away from the order, it would deal a blow to Montreal-based Bombardier, which has been scrambling to sell its CSeries jets but hasn't secured an order in more than a year.

Analyst Chris Murray of AltaCorp Capital said there's a slim chance Porter could use the CSeries jets to fly from Toronto's Pearson International Airport or other airports within its network. But the Toronto island airport was a critical component of the CSeries order for Porter, Murray said.

"Both the quantity that they ordered and the business case that they laid out for it really mandated using Billy Bishop as the core hub," he said.

The head of a Toronto community group opposed to expanding the island airport said the federal government's decision is the culmination of 2 1/2 years of citizen-led action.

"Minister Garneau's comments reaffirming the Liberal position remove any doubt -- the Island Airport expansion scheme is dead," said NoJetsTO chairman Norman Di Pasquale.

Bombardier has 603 CSeries commitments, including 243 firm orders. The plane, which is more than two years late and US$2 billion over budget, is awaiting certification from Transport Canada before entering into service by mid-2016.

The Quebec government has agreed to give Bombardier US$1 billion to help complete development of the CSeries in exchange for a 49.5 per cent stake in the project.

The provincial government has also made it clear that it would like to see Ottawa step up with funding, though Prime Minister Justin Trudeau said earlier this week that Bombardier would need to make a "strong business case" for such a request.