For months now, airlines have said that as travel began to slowly tick upward, they would heavily enforce the rule that all passengers must wear a face mask on board for the duration of the flight.

They weren’t kidding.

More than 700 passengers have been banned from flying U.S. domestic carriers since the mandate went into effect, according to a story in the Los Angeles Times.

It’s the airlines’ version of ‘No Shoes, No Shirt, No Service.’

Not surprisingly, Delta Air Lines has led the way. The Atlanta-based carrier has been more adamant, and more vocal, about passengers wearing face masks. As a result, Delta leads all carriers having placed 270 passengers on its “no fly” list, followed by United Airlines, with 150; Spirit Airlines, 128; Frontier Airlines, 106; Alaska Airlines, 78; and Hawaiian Airlines, six.

American and Southwest declined to disclose to the Times how many passengers they have banned.

“We expect our customers to comply with our policies when they choose to travel with us, and we take action when that is not the case,” American Airlines spokesman Curtis Blessing told the newspaper.

Airline representatives also said they did not share the names of those passengers they have banned with other carriers, meaning a passenger banned on one airline could ostensibly fly with another.

Airlines cannot monetarily fine violators because there is no federal regulation in place requiring passengers to wear face masks, leaving it up to each individual carrier. Sara Nelson, president of the Assn. of Flight Attendants-CWA, which represents nearly 50,000 flight attendants at 19 airlines, is one of many stakeholders in the industry asking for a federal mandate.

“Flight attendants want a federal mandate, and so do lawmakers,” she said. “Just like anyone smoking on a plane faces federal charges and fines, so too should people understand the serious consequences of putting the health of others at risk by refusing to wear a mask.”