That's true. I've never had to do anything but distribute them in the past. In this case I suppose I'm technically co-producer since the director, composer/sound designer and I are the only three on the production team. Nevertheless, it seems like there must always be something to keep people accountable. Apparently it's naive to expect them to pull their weight because of passion for the project, or even for pay!, if there aren't dire consequences.
I have been thinking about this topic for the last few days. It's true that you can create contracts that outline the expectations for both how actors will behave, and what the theatre will provide in return, but in truth, the actors have to
want to. They can want to for a variety of reasons: because it's their job, because they are getting paid, because they take pride in their work, because they love the company/show/director/ensemble, or some other reason.
The "dire consequences" are that you get replaced, and do not get paid. If they don't want to be in the show, I would replace them.
Now, if it's just a matter of them being late, there are some things that you can try - the primary thing is to talk to them about it. Figure out why they are late and see what can be done to fix it. But, missing rehearsals/leaving in the middle of rehearsal indicates to me that they don't want to be there.