Setting that Doesn't Allow Call Queue Memebers ot Opt Out of Call Queues

Trying to find the setting to stop users form opting out of call queues. 

I’ve tried to find any type of setting but haven’t been able to.

Users are opting out at night or PTO and staying opted out for days.

We will instruct them to put DND for lunch or other short opt out reasons and for PTO they will have to ask us.