The US is threatening the EU with $11 billion in sanctions over subsidies to Airbus\, just as its main rival Boeing endures its most difficult period in decades

The US is threatening the EU with sanctions on $11.2 billion in imports over subsidies to its largest aircraft maker, just as Boeing endures its most difficult period in decades in the fallout from two fatal plane crashes.

The US Trade Representative said on Monday that it the World Trade Organization found "repeatedly that European Union (EU) subsidies to Airbus have caused adverse effects to the United States."

Robert Lighthizer identified EU products, including wine, cheese, and Airbus aircraft, that could face tariffs when imported to the US.

The US government did not link the sanctions to Boeing's troubles, and cited a years-long dispute over subsidies. The optics of the move will nonetheless be noticed, especially as criticism mounts of the close relationship between Boeing and the US government.

The US first accused the EU of subsidizing aircraft made by France-based Airbus to the WTO in 2004, in a case that has yet to be resolved. The EU has also accused the US of subsidizing aircraft made by Boeing, and the TWO has found that both the EU and the US were giving improper subsidies.

Trade Representative Robert Lighthizer said on Monday that "This case has been in litigation for 14 years, and the time has come for action."

The list of items subject to tariffs will not be finalized until the WTO rules on a challenge from the EU, the statement said.

Lighthizer's statement comes as Boeing, Airbus' biggest rival, faces an ongoing crisis prompted by two air disasters.

Two similar accidents saw its 737 Max plane crash and kill everybody on board: one operated by Indonesian airline Lion Air and the other by Ethiopian Airlines.

The plane is one of Boeing's best-sellers but it has now been grounded around the world as Boeing works on a fix to its anti-stall software system.

Boeing announced on Friday that it will cut production of the plane from 52 planes a month to 42 as investors worry about the long-term impact of the crashes on the manufacturer.

An Indonesian airline tried to cancel its order for Boeing 737 Max aircraft, in the wake of the crash, while a Chinese aircraft leasing firm cancelled $5.8 billion in orders for the 737 Max.

China also signed a $34 billion order for 300 Airbus planes the day after it suspended the airworthiness certificate for the Boeing jets.

Boeing's crisis has also spread to the Federal Aviation Administration, where scrutiny has intensified over its practice of allowing Boeing to carry out much of government's regulatory work itself.

The crisis over the 737 Max crashes is Boeing's toughest period in decades. The company struggled during the 1970s recession, and had a difficult launch in the 2000s for its 787 Dreamliner. Christine Negroni, an aviation writer and the author of The Crash Detectives, told NPR that Boeing is in a tougher position now.

Boeing CEO Dennis Muilenburg, apologising last week after the crashes, said: "I cannot remember a more heart-wrenching time in my career with this great company."

The crisis, coupled with President Donald Trump's close relationship with Boeing, may also be threatening the reputation of the US as the leader in aviation, experts told Business Insider.

Michael Dreikorn, a former FAA official who also previously served as vice president of quality and compliance for the jet-engine maker Pratt & Whitney, told said he thought the FAA was taking a "credibility hit globally" as a result of the two crashes.

"The US's reputation can take a hit," he said. "And it probably should take a hit."

Get the latest Boeing stock price here.