Major international airlines cancelled flights heading to the US or changed the planes they’re using on Wednesday, the latest complication in a dispute over concerns that the new 5G mobile phone service could interfere with aircraft technology.

Carriers took widely different approaches to the brewing crisis affecting international travel, from Middle Eastern airline Emirates drastically reducing its US-bound flights to Air France saying it would fly as normal.

It wasn’t immediately clear why the airlines made those decisions — or whether they took into account that mobile carriers AT&T and Verizon agreed this week to pause the rollout of the new high-speed wireless service near key airports.

US officials had said that even with the concession, there could be some cancellations and delays because of limitations of equipment on certain planes.

Some airlines said on Wednesday they received warnings from the US Federal Aviation Administration (FAA) or Boeing that the plane maker’s 777 was particularly affected by the new wireless service.

It was also not clear how disruptive the cancellations would be. Several airlines said they would try to merely use different planes to maintain their schedules.

Similar mobile networks have been deployed in dozens of other countries — but there are some key differences in how the US network works that could make it more likely to cause problems for airlines.

The new 5G network uses a segment of the radio spectrum that is close to that used by radio altimeters, which measure the height of aircraft above the ground and help pilots land in low visibility. The US Federal Communications Commission (FCC), which sets a buffer between the frequency that 5G uses and the one that altimeters use, determined that it could be used safely in the vicinity of air traffic.

AT&T and Verizon have said their equipment will not interfere with aircraft electronics.

But FAA officials saw a potential problem, and telecom companies agreed to a pause on Tuesday while it is addressed.

On Wednesday, Emirates announced it would halt flights to several American cities due to “operational concerns associated with the planned deployment of 5G mobile network services in the US at certain airports”. It said it would continue flights to Los Angeles, New York and Washington.

“We are working closely with aircraft manufacturers and the relevant authorities to alleviate operational concerns, and we hope to resume our US services as soon as possible,” the state-owned airline said.

Tim Clark, president of Emirates, pulled no punches when discussing the issue. He told CNN it was “one of the most delinquent, utterly irresponsible” situations he’d ever seen as it involved a failure by the government, science and industry.

Of particular concern appears to be the Boeing 777. Emirates only flies this model and the Airbus A380 jumbo jet — and it was among one of the most affected airlines.

Japan’s All Nippon Airways said that the FAA “has indicated that radio waves from the 5G wireless service may interfere with aircraft altimeters.” It added that Boeing announced restrictions on airlines flying its 777s, and said it cancelled 20 flights over the issue to cities such as Chicago, Los Angeles and New York.

Japan Airlines similarly said that it had been informed there could be interference with the 777.

It said it will stop using the model in the continental US for now. Eight of its flights were affected on Wednesday.

Taiwan’s EVA Air also said the FAA specifically said 777s may be affected, but it did not spell out how it would adjust its schedule.

But Air France said it planned to continue flying its 777s into American airports. It did not explain why it didn’t change its aircraft as many other carriers had.

In a statement, Chicago-based Boeing Co said it would work with airlines, the FAA and others to find a solution that would allow all planes to fly safely as 5G is rolled out. It did not respond to questions about its 777.

Air India also announced on Twitter it would cancel flights to Chicago, Newark, New York and San Francisco because of the 5G issue.

But it also said it would try to use other aircraft on US routes — a course several other airlines took.

Korean Air, Hong Kong’s Cathay Pacific and Austrian Airlines said they substituted different planes for flights that were scheduled to use 777s. Korean Air spokeswoman Jill Chung said the airline was also avoiding operating some kinds of 747s at affected airports. Germany’s Lufthansa also swapped out one kind of 747 for another on some US-bound flights.

British Airways cancelled several planned US-bound Boeing 777 flights and changed aircraft on others.

The FAA has said it will allow planes with accurate, reliable altimeters to operate around high-power 5G. But planes with older altimeters will not be allowed to make landings under low-visibility conditions.

Among the problems that may make the 5G rollout an issue in the US and not other countries, according to the FAA, are that American towers use a more powerful signal strength than those elsewhere, the network operates on a frequency closer to the one altimeters use, and tower antennae point up at a higher angle.

“Base stations in rural areas of the United States are permitted to emit at higher levels in comparison to other countries which may affect radio altimeter equipment accuracy and reliability,” the FAA said in December.

France, for example, reduces the power of the networks near airports.

The FCC’s chairwoman said in a statement that 5G “deployment can safely co-exist with aviation technologies in the United States, just as it does in other countries around the world.” However, Jessica Rosenworcel urged the FAA to conduct its safety checks with “both care and speed.”

The European Union Aviation Safety Agency said it was “not aware of any in-service incidents caused by 5G interference.”

“Until the 5G initiation in the US, the technical data received from EU manufacturers offers no conclusive evidence for immediate safety concerns at this time,” it said.

AT&T and Verizon spent tens of billions of dollars for the 5G spectrum known as C-Band in a government auction last year.

Choi Jong-yun, a spokeswoman of Asiana Airlines, said the company hasn’t been affected so far because it uses Airbus planes for passenger flights to the US.

However, Choi raised a new wrinkle, saying airlines have also been instructed by the FAA to avoid automatic landings at affected US airports during bad weather conditions, regardless of plane type. Asiana will redirect its planes to nearby airports during those conditions, she said.