U.S. Customs and Border Protection has confirmed it’s requiring truck drivers to wear masks at all ports of entry, in keeping with an executive order issued by the Center for Disease Control and Prevention.

The agency has also clarified that truck drivers do not have to wear a mask when they are the only occupant of a commercial vehicle, but must do so when exiting the truck, entering a facility at a port of entry, or during a secondary inspection, the Canadian Trucking Alliance (CTA) reports.

The CTA says some of its members have raised questions about how team drivers are treated through the order. It continues to seek further clarification on the point.

Masks must completely cover the nose and mouth, and cloth masks should be made with two or more layers of a tightly woven, breathable fabric, the CDC says.

In addition to that, masks should be secured to a driver’s head with ties, ear loops or elastic bands that go behind the head. “If gaiters are worn, they should have two layers of fabric or be folded to make two layers,” the CDC adds.

The masks should also fit snugly against the side of the face, and be a solid piece of material without slits, exhalation valves, or punctures.

Further details about the mask attributes can be found here.