More than four-fifths of adults nationwide already have received at least one dose of a COVID-19 vaccine. But Biden contends his various workforce vaccine mandates are an important step in curtailing the virus, which has killed more than 780,000 people in the U.S.
Opponents have taken a three-tiered approach to challenging Biden's requirements. In lawsuits, they contend the vaccine mandates were imposed without proper public comment, were not authorized by Congress and infringe on states' rights to regulate public health matters.
"The reasoning across the cases is basically the same, which is that these statutes don't give the president or the agency in question the authority to issue the mandates," said Gregory Magarian, a constitutional law professor at Washington University in St. Louis.
The Biden administration contends its rule-making authority is firm and supersedes any state policies prohibiting vaccine requirements. Recent experience shows that such mandates generally prompt people to get vaccinated. By the time a Biden requirement for federal workers to be vaccinated took effect last month, 92% had received at least their first dose of the shot.
Following is a rundown of some of Biden's most sweeping vaccine requirements and the status of the legal fights over them.