CVS, the country’s largest pharmacy chain, is currently not offering Covid vaccines in 16 states, including Florida, New York and Pennsylvania, even to people who meet newly restricted criteria from the Food and Drug Administration.

Amy Thibault, a spokeswoman for CVS, cited “the current regulatory environment” as the reason the vaccine was not available in those states, or in the District of Columbia, emphasizing that the list could change. Legal experts said that federal decisions were creating an extremely difficult situation for pharmacies to navigate.

In some states, pharmacists are forbidden to administer vaccines that are not recommended by the Advisory Committee on Immunization Practices, a Centers for Disease Control and Prevention panel.

Last year, the panel voted to recommend updated Covid vaccines in June. In 2023, it endorsed new Covid vaccines in September, just one day after the F.D.A. gave its approval.

But as of this Thursday, the panel was not scheduled to meet for another three weeks. And, after a slew of high-level resignations at the C.D.C., Senator Bill Cassidy — Republican of Louisiana and the chairman of the Senate’s health committee — has called for the meeting to be “indefinitely” postponed. That could mean many people’s access to shots remains hamstrung well into the fall, when infections from respiratory viruses normally spike.

CVS will make the vaccines available nationwide if the advisory panel recommends them, Ms. Thibault said. But since the panel hasn’t yet made a decision, the company is holding off in states where it believes its pharmacists need a C.D.C. endorsement.