cnn's pete montini joins us. >> reporter: jake, airlines can essentially prevent a passenger from boardingrd, it's a different story. they want to avoid confrontation at all costs. this memo was sent to flight attendants and pilots, it outlines some exceptions for health rules but, quote, if the customer chooses not to comply for other reasons, please encourage them to do so but do not escalate further. likewise, if a customer is frustrated by another customer's lack of face covering, please use situational awareness to de-escalate the situation. the unanimous message from airlines, jake, is do not get into situations where flight attendants have to boot passengers off a flight or even worse, turn an airplane around and land. airlines are doing all of this in the absence of a requirement from the federal government. >> in the absence of leadership, really. united airlines is an airline trying to keep the middle seats of their planes empty, despite some photos we've seen of crowded flights. what happens if a customer booked on a flight wants a refund? >> reporter: it's important to note tha