Sort of. If the music stops and they're not running classes anymore, you would have a legal case to require them to do a special class for you...if you forced the issue. Most likely they would just pay you as a captain until the next class if you forced the issue but that wouldn't make you whole if you're at a regional and need pic time.

Reality in this case...This is one of those rare times when you need to accommodate the airline's schedule. Either move the drills or do a later upgrade class. Unless your unit is working up for a deployment in the near term, they need to recognise that this is one of those things when they need to be flexible.