The U.S. agency that regulates workplace safety issued guidance on Friday urging employers to require many fully vaccinated workers to wear masks to protect unvaccinated colleagues and customers, amid a surge in COVID-19 cases.

The Occupational Safety and Health Administration (OSHA) recommended that workers wear masks “in areas of substantial or high community transmission,” such as manufacturing plants, meat processing facilities and retail establishments, unless they have medical conditions that make it difficult to wear a face covering.

Employers should also consider staggering the times workers clock in and out of work and take breaks to prevent large groups of people from congregating, OSHA said. High-volume retail businesses should ask customers to wear masks and consider requiring them. The agency had made similar recommendations last year, early on in the pandemic.

The updated guidance comes as COVID-19 cases are on the rise across the U.S., particularly in areas where large numbers of people remain unvaccinated. Some preliminary studies have shown that vaccinated people are still capable of spreading the highly contagious Delta variant of the coronavirus.

An increasing number of employers have said they will require at least a part of their U.S. workforce to be vaccinated. Walmart, Uber, McDonald’s and DoorDash have adopted mandates for corporate employees, and many airlines and technology companies are requiring employees to be vaccinated.

Thursday’s guidance, which is not legally binding, was issued after the U.S. Centers for Disease Control and Prevention late last month recommended that fully vaccinated individuals resume wearing face masks in public.

OSHA on Friday also said an emergency rule it adopted in June requiring healthcare employers to mandate use of face masks, ensure proper ventilation and limit the number of patients and visitors is “more important than ever” and will remain in place for the time being. The agency said it would revisit the requirements next month.