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

Some airlines said they were warned that the Boeing 777, a plane used by carriers worldwide, was particularly affected by the new high-speed wireless service.

The aircraft is the workhorse for the Dubai-based Emirates, a key carrier for East-West travel, and its flight schedule took one of the biggest hits.

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

The cancellations and changes came a day after mobile phone carriers AT&T and Verizon said they would postpone new wireless service near some US airports planned for this week.

The US Federal Aviation Administration (FAA) has cleared a number of aircraft to fly into airports with 5G signals, but the Boeing 777 is not on the list.

Similar mobile networks have been deployed in dozens of other countries — sometimes with concessions such as reducing the power of the networks near airports, as France has done.

But in the US, the issue has pitted the FAA and the airlines against the Federal Communications Commission (FCC) and telecommunications companies.

The 5G service uses a segment of the radio spectrum that is close to that used by radio altimeters, which are devices that measure the height of aircraft above the ground and help pilots land in low visibility.

The FCC, which set a buffer between the 5G band and the spectrum that planes 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 the telecom companies agreed to a pause while it is addressed.

On Wednesday, Emirates announced it would halt flights to several US cities due to “operational concerns associated with the planned deployment of 5G mobile network services in the U.S. 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.

Of particular concern appears to be the Boeing 777. Emirates only flies that model and the Airbus A380 jumbo jet.

Japan’s All Nippon Airways said that the FAA “has indicated that radio waves from the 5G wireless service may interfere with aircraft altimeters”.

“Boeing has announced flight restrictions on all airlines operating the Boeing 777 aircraft, and we have cancelled or changed the aircraft for some flights to/from the US-based on the announcement by Boeing,” ANA 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 that 5G signals “may interfere with the radio altimeter installed on the Boeing 777”.

It said it will stop using the model in the continental US for now.

Eight of its flights were affected Wednesday — three passenger trips and five for cargo.

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 Boeing 777s into American airports. It did not explain why it didn’t change its aircraft as many other carriers have.

Chicago-based Boeing Co did not immediately respond to a request for comment.

Air India also announced on Twitter that 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.

Contributing to the problem, according to the FAA, are the signal strength of the 5G towers and the orientation of their antennae.

“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.

FCC Chairwoman, Jessica Rosenworcel said in a statement that the 5G “deployment can safely co-exist with aviation technologies in the United States, just as it does in other countries around the world.”

However, Rosenworcel urged the FAA to conduct its safety checks with “both care and speed”.

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 for 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.