In a country where COVID-19 remains out of control, it’s wrong for anyone not to wear a mask on a commercial airplane. Increasing evidence shows that good cloth face coverings significantly lower the spread of the novel coronavirus at close quarters – and that not wearing them is risky, because this germ is so often breathed into the air by people who don’t yet know they have it. One passenger on a flight from Singapore to Hangzhou, China, was infected by neighboring passengers when he merely let his mask slip below his nose while talking with his family.

It is one thing for people to take chances with their own health. It’s quite another when their reckless behavior also puts others at risk. The evidence clearly shows that this is the case with masks during the pandemic. In fact, people who choose to risk their own health this way are exposing others to potentially worse danger. Smoking is banned almost everywhere – including on airplanes. During the pandemic, all air passengers should be required to wear masks, and face legal penalties if they don’t.

Most Americans have come to understand the need to mask up. Seventy-two percent usually do. But 18 percent rarely or never do, and some of these objectors apparently want to remain maskless on airlines. This imperils the health of innocent strangers, including flight-crew members for whom the cabin is a workplace. Airplane ventilation systems remove almost all germs from the air, but it takes a few minutes for exhaled virus particles to reach the filters.

Major airlines already require passengers and crew members to wear masks, but their rules come with exceptions (one airline excuses children under age 8, for instance) and, most important, aren’t always enforced. In a couple of instances airlines have refused entry to unmasked passengers or removed someone from a plane after boarding, but as things stand there’s not much they can do to keep irresponsible passengers from removing their masks during flight.

A Federal Aviation Administration rule could set penalties for noncompliance – just as some governments do. Many cities where the coronavirus is uncontained are levying $100 fines for going without a mask near other people in public places. Research has shown that such mandates work. Enforceable mandates increase the number of mask wearers and reduce new infections. If 95 percent of Americans were to wear masks, more than 30,000 lives could be saved over the next few months, according to the University of Washington’s Institute for Health Metrics and Evaluation. When masks do not prevent transmission altogether, they make infections less severe. And they do so without appreciably limiting people’s intake of oxygen.

Air travel is still a fraction of what it was before the pandemic. For airlines, as for the U.S. at large, it will be impossible to return to normal unless COVID-19 is contained. Masks are one of the most effective strategies. Democrats in the House have introduced legislation that would authorize the FAA to require masks on all U.S flights and impose criminal penalties for failure to comply. It should be passed without delay.