CNN Business  — 

The nation’s biggest cellular carriers say they won’t further delay the rollout of 5G wireless service near airports — ratcheting up tensions between transportation officials and the telecom industry ahead of a critical deadline this week that could trigger widespread US flight delays and diversions.

In a letter Sunday reviewed by CNN, the CEOs of Verizon and AT&T (which owns WarnerMedia, CNN’s parent company) offered to implement similar restrictions on their 5G antennas as those used near French airports, for six months. But they rebuffed calls by the Transportation Department and the Federal Aviation Administration to push back the Jan. 5 start date for 5G service on an important set of radio frequencies known as the C-Band.

“At its core, your proposed framework asks that we agree to transfer oversight of our companies’ multi-billion dollar investment in 50 unnamed metropolitan areas representing the lion’s share of the U.S. population to the FAA for an undetermined number of months or years,” the companies wrote. “Agreeing to your proposal would not only be an unprecedented and unwarranted circumvention of the due process and checks and balances carefully crafted in the structure of our democracy, but an irresponsible abdication of the operating control required to deploy world-class and globally competitive communications networks.”

The carriers had previously pushed back the start date from Dec. 5, 2021 to Jan. 5, 2022.

Transportation officials and the aviation industry have expressed concerns about the possible impact that 5G transmissions may have on radar altimeters, aircraft equipment that relies on radio signals to tell pilots how far they are from the ground.

In December, the FAA issued an urgent warning saying it planned to ban the use of radar altimeters in low-visibility conditions around airports where 5G antennas were installed, saying the potential for interference could disrupt landings in some circumstances. The agency did not specify at the time which airports would be affected by the rule, but estimated that the restrictions could lead to thousands of aircraft being affected and warned of mass disruptions to air travelers. Aviation industry groups echoed those warnings of an impending crisis, saying hundreds of thousands of flights and tens of millions of passengers could be diverted or delayed.

“Without appropriate mitigations, the 5G deployment around airports could disrupt as many as 345,000 passenger flights — impacting 32 million travelers — in addition to 5,400 cargo flights each year in the form of delays, diversions or cancelations,” said Carter Yang, a spokesperson for Airlines for America, a trade group representing US passenger and freight airlines. “We continue to urge the FCC and the telecom industry to work with the FAA and the aviation industry on a practical solution that will enable the rollout of 5G technology while prioritizing safety and avoiding any disruption to the aviation system.”

But the Federal Communications Commission, which oversees the use of radio airwaves in the US, has concluded after several years of study that there is little risk of interference, as the frequencies used by radar altimeters are separated from the frequencies used for 5G by more than 200 megahertz of blank “guard band” spectrum. The aviation industry and the FAA also participated in the FCC’s review process that ultimately led to the approval of 5G in the C-Band in 2020.

Telecom industry groups have said 5G in the C-Band frequencies has already been deployed worldwide, and that there have been no reported incidents anywhere involving 5G and aircraft.

“The laws of physics are the same in the United States and France,” AT&T and Verizon wrote on Sunday. “If U.S. airlines are permitted to operate flights every day in France, then the same operating conditions should allow them to do so in the United States.”

The FAA and DOT didn’t immediately respond to a request for comment.