The short answer is that this MAY BE legal, provided that: a. The company can show it has a compelling need to require proof of vaccination; b. It doesn’t ask for any other protected health information; and c. It accommodates employees, not only those with disabilities, e.g., conditions making them allergic to vaccines, and religious protests, but also practical common sense. So, for example, vaccines are in short supply and it would be unfair to deny an employee who wants and hasn’t been able to get both shots. Here’s a story that breaks it down into more detail. Hope it helps.