I'm assuming the 'mandatory' part is being enforced by the management of the facility, and not those higher up? Often it seems the management of these places are on power trips and have no common sense (My wife used to work in a lot of them).
I would put it to them that they are breaching the minimum rest periods and to rearrange for them. Don't get nasty, they will use it against you. Just state the minimum rest, and it is unreasonable given the assigned hours to expect said person to attend. If they get arsey, inform them you are making an official complaint. (It really shouldn't need to go that far.)
Honestly, some of the places my wife has worked in, the management are educated but totally clueless e.g. Refusing to order safety gloves for workers even though they work with patients who A) are covered in bodily discharged B) Some who have MRSA (!).
Main point, tell X not to be aggressive or confrontational, just be matter of fact. I won't be attending the meeting/training due to the minimum legal rest period regulation (or whatever it's called.), and will have to be arranged for another time. I almost guarantee that others will not turn up anyway.
The downside is that they may arrange the training on X's day off.