When I worked at
Disneyland a million years ago as a Ride Operator we were in the Teamsters union. Yes, you had to work a certain number of hours a certain number of weeks in a row to get benefits. And yes, as soon as you would get close they would cut your hours so you couldn't get them. Back then it was a big deal if you got benefits and not many people had them. If they are still doing that with the hours then I can see why they would be upset about it becoming even more difficult to get them.
It's not like they always work 25 hours a week and are complaining they don't get benefits. You could work 50 hours a week for months and then just as you get close to the amount of weeks you need they would drop you to 24 hours a week (Fri, Sat, Sun only) for awhile. Then it would go back up.
There were threats of strikes a couple of times when I was there and I always voted for them because I wanted time off and I wanted to see what would happen if their was a strike. I was just a teenager then though

It never happened though and I don't think it will this time either. I think the last one was in the early '80s and I hear it was a disaster. I don't think either side really wants a strike.