DETROIT — Unionized auto workers in the U.S. will go back to wearing masks in all factories, offices and warehouses starting Wednesday because of the spreading delta coronavirus variant.

The decision by a task force of representatives from General Motors, Ford, Stellantis and the United Auto Workers was announced on Tuesday. It includes all workers regardless of whether they’ve been vaccinated.

The move comes just under a month after vaccinated union workers were allowed to shed their masks. But the union says in a statement the decision was made for worker safety due to a change in Centers for Disease Control and Prevention mask guidelines. The statement says the delta variant’s “alarmingly high” transmission rate is making the return of masks necessary.

The task force encourages all workers to get vaccinations so mask requirements can be relaxed. About 150,000 factory workers from all three companies wore masks at work from May 2020 until the requirement ended July 12.

“We will continue to closely monitor this situation to ensure we are doing everything possible to keep our families, members and employees safe,” the union said in a statement.