If it is a trial, you also have to give agreement to participate.
I clearly remember a number of 230 aircrew in the 80s getting very exercised by the introduction of blood tests into the annual medical.
Much "They can't do this to us, we have rights" was going on in the crewroom. I seem to recall that the 2i/c was Boss at the time, due to an indiscretion on the part of the actual Boss.
On hearing the whiney noises, Pete C simply 'edicted', "OK, no jab, no medical cat. No cat, no fly, no fly no flying pay".
Problem solved. Seemingly it's not a democracy (or wasn't).
CG