majority of the traveling and shipping public will essentially be grounded. facing cancellations, diversions or delays. this is reckless, it s dangerous and it s got to stop. take a pause. this is not a cellphone signal and we re focused on protecting lives. reporter: the cellphone industry insists there is no 5g risk to planes, recently telling nbc news 5g networks operate safely without interference in nearly 40 countries around the world and it will be no different here. transportation secretary pete buttigieg. look, the wireless carriers are impatient to deploy technology that stands to make a big impact, a positive impact on our economy, but on the aviation side we ve also got to make sure that it s safe. reporter: the airlines this morning are warning that they could be forced to ground large numbers of planes because those planes are not yet certified to operate around 5g sites. government aviation sources say as this system goes live tomorrow, we could see mass