From what I've seen the conversation is a lot more nuanced. It's not "yes AI" vs "no AI." It's more around can you use my likeness, writing, or artwork to train AI with minimal to zero compensation (what studios want) or with compensation structure both sites negotiate (what unions what). Or can the result of AI be used to undermine labor. Currently, the output of AI isn't up to expected standards for much of anything. Studios are obviously trying to use that output to replace "writing credit" which has a historical structure with higher compensation. The person they pay to go "punch it up" won't get that. The resulting product would be mostly the same, but the person polishing and finishing it does a lot more work with less compensation.
AI is also just a relatively minor part of what unions are trying to negotiate.