IANAL: Would said requirement need to be found unconstitutional in order to prevent mandating vaccine in prisons, where prisoners are literally a captive audience? The two stakeholders comprise at least prisoners & guards. What legal hurdles would such a vaccination mandate face?
CONTEXT: The headline US prison guards refusing vaccine despite COVID-19 outbreaks indicates: Prison guards are refusing coronavirus vaccines at alarming rates..
UPDATE: September 2021: "My job as president is to protect all Americans," Mr. Biden said Thursday. "So tonight, I'm announcing that the Department of Labor is developing an emergency rule to require all employers with 100 or more employees that together employ over 80 million workers to ensure their workforces are fully vaccinated or show a negative test at least once a week." reference link / source