By David Shepardson and Allison Lampert

WASHINGTON/MONTREAL, Jan 29 (Reuters) - President Donald Trump said on Thursday the U.S. was decertifying Bombardier Global Express business jets and threatened 50% import tariffs on all aircraft made in Canada until the country's regulator certified a number of planes produced by U.S. rival Gulfstream.

"If, for any reason, this situation is not immediately corrected, I am going to charge Canada a 50% Tariff on any and all aircraft sold into the United States of America," Trump said of the Gulfstream certification process in a post on Truth Social.

  His declaration came amid broader tensions between the neighboring countries after Canadian Prime Minister Mark Carney, citing U.S. trade policy, last week urged nations to accept the end of the rules-based global order that Washington had once championed. 

Trump also said he was "decertifying their Bombardier Global Expresses, and all Aircraft made in Canada" until the Gulfstream planes were certified. 

That threat, if carried out, would have a drastic impact on U.S. carriers like American Airlines and Delta Air Lines, which rely on Canadian-made airplanes for many of their regional services. 

However, a White House official told Reuters that Trump was not suggesting decertifying Canadian-built planes currently in operation. U.S. airline officials told Reuters that FAA officials had made similar statements. 

Data provider Cirium said there were 150 Global Express aircraft in service registered in the U.S., operated by 115 operators and 5,425 total aircraft of various types made in Canada in service registered in the U.S. including narrowbodies, regional jets and helicopters.

Montreal-based Bombardier said it had taken note of Trump's post on social media and was in contact with the Canadian government. "We hope this is quickly resolved to avoid a significant impact to air traffic and the flying public," it said.

Airline officials said if the U.S. could decertify airplanes for economic reasons, it would give other countries a powerful weapon and could put the entire aviation system at risk.

“Mixing safety issues with politics and grievances is an incredibly bad idea,” said Richard Aboulafia, managing director of U.S. aerospace management consulting firm AeroDynamic Advisory.

Delta declined to comment. American Airlines, General Dynamics-owned Gulfstream and Carney's office did not immediately respond to requests for comment.  

PATH TO DECERTIFICATION UNCLEAR

Bombardier operates multiple service centers in the United States and has a facility in Wichita, Kansas, where it is growing its defense business. The U.S. is the world's largest market for business aviation and the Canadian company has about 3,000 employees based there.

IAM, a union representing more than 600,000 workers in North America and thousands of workers in the air transportation and aerospace sector, said Trump's threats "would cause serious disruption to the North American aerospace industry and put thousands of jobs at risk on both sides of the border."

It was unclear what planes beyond Bombardier's Global large-cabin jets would fall under Trump's increased tariffs, including the Airbus A220 commercial jets made in Canada. Most A220 jets operated by U.S. carriers are produced at an Airbus production line in Mobile, Alabama.

Trump said Canada has refused to certify the Gulfstream 500, 600, 700, and 800 jets. In April, the Federal Aviation Administration and the European Union Aviation Safety Agency certified the Gulfstream G800 jet. Transport Canada, which is responsible for Canadian certification, did not respond immediately to a request for comment.

It was unclear how Trump would decertify the planes since that is the job of the Federal Aviation Administration, but he has made similar declarations in the past that were ultimately carried out, often with exemptions, by relevant agencies.

It does not appear the FAA has the legal authority to revoke certifications for planes based on economic reasons, as it can only do so for safety reasons under existing regulations. The FAA declined immediate comment.

CERTIFICATION PROCESS

Under global aviation rules the country where an aircraft is designed - the U.S. in Gulfstream's case - is responsible for primary certification known as a type certificate, vouching for the design’s safety.

The FAA in December certified Bombardier's Global 8000 business jet, the world's fastest civilian plane since the Concorde with a top speed of Mach 0.95, or about 729 mph (1,173 kph). It was initially certified by Transport Canada on November 5.

Other countries typically validate the decision of the primary regulator, allowing the plane into their airspace, but have the right to refuse or ask for more data. Following a Boeing 737 MAX crisis, European regulators delayed endorsement of some U.S. certification decisions and pressed for further design changes, sparking tensions with the FAA.

Due to U.S. tariffs on key Canadian imports, Carney is pushing to diversify trade away from the United States, which takes around 70% of all Canadian exports under terms of the U.S.-Mexico-Canada free trade deal.

(Reporting by Bhargav Acharya in Toronto, David Shepardson and Jasper Ward in Washington, Allison Lampert in Montreal, Tim Hepher in Paris and Rajesh Kumar Singh in Chicago; Editing by Jamie Freed)