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Starting Monday, riders on all Los Angeles Metro trains and buses will have to wear face coverings to curb the spread of the coronavirus as the county gradually moves towards reopening certain businesses, the transportation agency announced Thursday.

Previously, L.A. Metro was only recommending that riders wear face coverings, and employees have spoken out about not feeling protected enough as they worked in one of the country’s busiest transit systems while the virus spread.

Earlier this week, L.A. County Supervisor Janice Hahn wrote a letter to Metro CEO Phillip Washington, saying that the agency should immediately require face coverings.

“The latest Los Angeles County Public Health Order requires that face coverings be worn in grocery stores and other essential businesses,” she wrote. “Transit is considered essential infrastructure, however Metro has chosen to encourage bus and rail passengers to wear face coverings rather than requiring them to.”

It’s still unclear how L.A. Metro will enforce the new mask requirements.

“As we prepare to restore bus and rail service that has been reduced due to the COVID-19 crisis, we want transit to be as safe as possible,” Washington said in a written statement. “The enforcement of this new requirement will be a work in progress, but we are committed to doing everything within our power to protect both the public and our employees.”

In a news conference earlier Thursday, L.A. County’s public health director Barbara Ferrer said that most people in the county have been complying with requirements to wear face masks.

“If you’re a daily rider, do your part: cover your face and help us all protect your life and the lives of everyone who critically depends on our transit system for essential rides,” city of Inglewood Mayor and Metro Board Chair James Butts said in a statement.

It’s not only the L.A. Metro transportation system requiring the masks.

L.A. Mayor Eric Garcetti announced Wednesday that all riders on the Los Angeles Department of Transportation’s DASH, Commuter Express and Cityride buses must also wear protective face coverings.

“It is very important that everybody take this step and cover their faces on buses so that other riders and bus operators can stay healthy,” he said.

Everyone flying through Los Angeles International Airport must also wear face masks.

Since the beginning of the coronavirus crisis in the county, L.A. Metro has made several changes to its operations as ridership dwindled with the mandated stay-at-home orders.

Trips were scaled back, bus operators were given plexiglas shields, frontline employees were given personal protective equipment, hand sanitizer dispensers were installed at major transit stops and stations and passengers were only allowed to board buses from the rear doors, according to the agency.