Dr. Anthony Fauci supports businesses choosing to leave mask mandates in place because the “issue,” he said, is that “we don’t have any way of knowing who is vaccinated.”

Fauci believes it is “perfectly reasonable and understandable” for businesses to keep mask mandates in place despite recent Centers for Disease Control and Prevention (CDC) guidance relieving vaccinated individuals from wearing masks in most settings.

“The problem and the issue is that we don’t have any way of knowing who is vaccinated and who’s not vaccinated,” Fauci said during an appearance on Good Morning America.

“I think that’s where the confusion arises because there are some establishments who are saying, ‘Well, I’m going to have people coming into my establishment or my store or what have you. Some are going to be vaccinated, some are not. I’m not going to know the difference,’” he continued.

“Some might be infected and might actually have a risk of infecting someone else,” he added. “And under those circumstances, it’s perfectly reasonable and understandable for the owner of that establishment to say, ‘You know, we’re going to keep the mask mandate up.’ And that’s what we’re seeing”:

Some major retailers have, by contrast, lifted their hardline mask mandates following the CDC’s updated guidance, including Target and Walmart.

Target, for example, announced on Monday the end of its store policy requiring all customers to wear masks.

“Given the CDC’s updated guidance last week, Target will no longer require fully vaccinated guests and team members to wear face coverings in our stores, except where it’s required by local ordinances,” the company said in a statement, adding that it will continue to “strongly” recommend unvaccinated individuals to wear face coverings. However, customers will not be asked to provide proof of receiving a vaccine. Home Depot is also following suit, dropping the mask requirement for vaccinated customers.

Over 123 million people in the U.S. are considered “fully vaccinated,” per the CDC’s May 17 data.