All passengers traveling through Seattle-Tacoma International Airport will be required to wear cloth face coverings starting May 18 to slow the spread of coronavirus, the Port of Seattle announced Saturday evening.

The requirement also applies to airport workers, including Port of Seattle employees, and airport visitors who aren’t flying. People who can’t tolerate facial coverings for medical reasons, as well as very young children, will be exempt.

The announcement follows requirements from major airlines and some airports that all passengers wear masks. Philadelphia International and Los Angeles International airports, for example, will both require all passengers and visitors to wear masks starting Monday. Denver International Airport started requiring all passengers to wear face coverings this past week.

Airlines including Seattle-based Alaska Airlines have set policies that make coverings mandatory for passengers when they’re on the plane.

It’s unclear how the Port of Seattle will enforce the requirement for passengers — about 3,800 people pass through the airport daily — and other visitors. The Port will refine its policies this week, spokesman Peter McGraw said Saturday by email.

The Transportation Security Administration (TSA) announced in the last week that workers at all its screening checkpoints, including those at Sea-Tac, will be required to have masks. At Sea-Tac, seven TSA employees have tested positive for COVID-10. Nationwide, 516 TSA employees have tested positive and five have died after contracting the virus.

The Port has provided masks for front-line workers like janitors and airport guides, but they haven’t been required to wear them.