The United Auto Workers Union (UAW), Ford, General Motors, and Stellantis have together agreed to require workers at auto plants represented by the union to wear masks. The decision, the quartet said, is in response to new guidance from the Center for Disease Control and Prevention (CDC).

The CDC recently changed its guidance for mask use for fully vaccinated people in the U.S. The organization said that the Delta variant of COVID-19 means that people in indoor spaces in places with substantial or high community transmission rates should use masks regardless of their vaccination status. It also said that 80 percent of the U.S. counties are now considered to have substantial or high community transmission rates.

The UAW and the three automakers (who call themselves the COVID-19 Joint Task Force) eased mask mandates in July, announcing that fully vaccinated workers were not required to wear them on the line as of the 12th. As cases rise, though, the four parties are readjusting their guidance.

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“While we know that masks can be uncomfortable, the spread of the Delta variant and recent data outlining the alarmingly high rate of transmission among those unvaccinated is a serious health threat,” wrote the UAW in a statement.

The COVID-19 Joint Task Force will not require workers to be vaccinated in order to work, but has strongly urged workers to get the vaccine, calling it the best way to get back to lifting mask mandates.

“We know that the best way to fight this virus is by getting vaccinated,” wrote the UAW. “The Task Force is strongly encouraging all members, coworkers and their families to roll up their sleeves so we can move more quickly on once again relaxing mask protocols. The more our members, coworkers and their families are vaccinated, the quicker we can vanquish this deadly pandemic.”