A more sensible approach is to encourage employees to choose the vaccination even if that means incentives. To terminate an existing employee for not being vaccinated particularly if there are medical grounds falls squarely in discrimination.
Discrimination tends to mean prejudicial treatment of people because of a characteristic that they have no choice in and cannot change. You know, like being disabled. Please don't confuse it with being treated differently on account of one's beliefs being shaped by what was on the internet this morning. Ultimately they can choose to get the vaccine, so discrimination it is not, unless, as you say, they cannot get vaccinated for medical reasons (being vulnerable to manipulation by Facebook doesn't count). All of the mandates that I have read about so far make specific exemptions for people who are genuinely unable to be vaccinated.