Airlines around the world are adjusting their schedules and aircraft deployments for flights to the U.S. over fears that a 5G rollout by AT&T Inc. and Verizon Communications Inc. near American airports could interfere with key safety systems.

Dubai’s Emirates said it will suspend flights to several U.S. cities, including Chicago, Newark and San Francisco, while Japan Airlines Co. and ANA Holdings Inc. said they won’t fly their 777 jets to and from the U.S. mainland after a warning from Boeing Co. about how the model’s altimeter will be affected.

British Airways cancelled a handful of services to the U.S. on Wednesday, and has also made some aircraft substitutions, a spokeswoman for the carrier said. The U.K. airline was using Airbus SE A350 and Boeing 787 jets to operate some flights usually flown by 777s, according to tracking website FlightRadar24. Singapore Airlines Ltd. will also substitute 777s for A350s, the carrier said in a statement.

Korean Air Lines Co. said its 777 and 747-8 aircraft are affected by the 5G service, and is rearranging its fleet. Air India Ltd. also warned flights to the U.S. will be curtailed or revised from Jan. 19.

Flights operated by the 777 and 747-8 were particularly affected after Boeing alerted operators of its two largest jetliners that they might not be able to safely land at American airports where 5G signals are present, Bloomberg News reported, citing a person familiar with the matter.

The concerns stem from potential interference with sensitive navigation equipment used during landings in poor weather, which a trade association representing major U.S. airlines said could lead to “catastrophic disruptions.” Frequencies within the so-called C-band being used for the 5G services are near airwaves used by aircraft radar altimeters, which track altitude and allow landings in bad weather. They also feed multiple critical safety systems.

At least 25 flights operated by Boeing 777 jets to the U.S. were canceled for Wednesday, according to data from Flightradar24.com. Deutsche Lufthansa AG switched its aircraft to the 747-400 from 747-8 on the Frankfurt-Chicago route.

Qatar Airways continues to operate all of its flights on 12 U.S. routes as scheduled, with only minor delays expected on some return services to Doha, a spokesperson for the carrier said.

AT&T and Verizon agreed late Tuesday to delay switching on hundreds of 5G cell towers near U.S. airports following last-minute talks with government officials over safety concerns. The companies, which spent more than $80 billion in a government auction last year for the rights, didn’t provide details on how long the suspension might last or the size or the zone around airports.

The Federal Communications Commission approved the transfer of the frequencies from other uses to the wireless companies last year after concluding there was no threat to aviation safety.

“The U.S. made all possible spectrum available on a licensed basis to telecom operators,” said Vivekanand Subbaraman, an associate vice president at Ambit Capital in Mumbai. “Other countries have not done that. That’s why it’s turning out to be a U.S.-specific issue.”

President Joe Biden said Tuesday the agreement will avoid “potentially devastating disruptions” to passenger travel, cargo operations and a recovery in the economy. Delta Air Lines Inc. still said it was preparing for possible weather-related cancellations starting as early as Wednesday if 5G signals cause limited interference with altitude instruments under certain conditions.

American Airlines Group Inc. didn’t immediately comment on the status of 777 flights scheduled Wednesday.