As the COVID-19 pandemic decimates demand for air travel, U.S. carriers have taken several unprecedented steps to increase onboard safety. The latest: urging passengers to wear face masks.

The world’s largest carrier, American Airlines, said Monday passengers will be handed a mask and hand sanitizer when boarding some flights, starting in early May. Travelers will be urged to follow Centers for Disease Control and Prevention guidelines to wear a face mask, but the airline won’t require masks onboard.

“We are looking out for our customers’ well-being to give them peace of mind while they travel with us,” Kurt Stache, American Airlines senior vice president of customer experience, said in a statement.

The program will be expanded to all flights based on the supply of masks and sanitizer, airline representatives said.

JetBlue went further, announcing Monday that all passengers will be required to wear face coverings during travel.

“Wearing a face covering isn’t about protecting yourself; it’s about protecting those around you,” said Joanna Geraghty, JetBlue’s president and chief operating officer. “This is the new flying etiquette. Onboard, cabin air is well circulated and cleaned through filters every few minutes, but this is a shared space where we have to be considerate of others.”

American, JetBlue, United, Delta and Frontier airlines have all begun requiring flight attendants to wear masks while performing their duties in the air. Some airlines are requiring masks for all employees who can’t keep 6 feet away from other workers and passengers.

Atlanta-based Delta Air Lines is employing some maintenance technicians, normally paid to maintain planes, to assemble cloth safety masks for Delta workers, with a goal of making 2,500 masks a week. Some of the material for the masks will come from discontinued T-shirts from Delta’s uniforms.

The changes come only a few days after the Association of Flight Attendants wrote to U.S. Transportation Secretary Elaine Chao and Health and Human Services Secretary Alex Azar, requesting that masks be mandated for flight crew, airline employees and passengers. The union represents about 50,000 flight attendants from more than 20 airlines.