Here's my take:
You treat those employees who didn't show for work *exactly* according to existing policy. If there is no policy, then you can't take action this time.
If the policy says a no-show, no-call is terminable, then do it. If it says the employee gets written up, then do it. And you definitely take the day away from any accrued comp days earned...no freeebies. If you make it OK for some, then you have to let anyone no-show anytime they want to spend the day at a political rally or function. It'll just spiral.
If the employee followed procedure, requested the time and it was charged against accrued comp time, then that's OK.
The business, in my opinion, has no obligation to support ideological or political causes on behalf of the employees. Fairness dictates that the employees not be actively or spitefully prevented from doing as they choose with their time, but the business has every right to expect that company policy applied on May 1 just like it does every other day of the year.
If you run a business in an "at-will" state, then you only need avoid doing anything that is illegal...discrimination, harassment, physical abuse, etc... Disciplining or terminating an employee for blatant contempt for company policy is not legally actionable.
All this should be balanced against the good advice to look at the cost-benefit...be careful with a big producer who is usually a good, compliant employee...it can be worth it to be flexible. Don't bother with the others.
Frankly, I think this is going to blow up in their faces. The demonstrations and marches, and the message itself, is not winning any friends with the majority of folks in the country, as far as I can tell. Besides, everybody is confusing the issue so badly it's scary. The issue is not immigration itself, but a) reform to the system to make it more realistic and navigable, and b)
dealing with those who break the law. Just because they broke the law running the border, instead of a red light, doesn't change a damn thing.
Since the protesters seem to feel that they are entitled to interpret the law in a way that's convenient to what they want, I figure I'll do the same and go help myself to whatever they have in their homes while they're demonstrating. I mean, 'no human being is illegal', right? I'm entitled, right?
If it's OK to flaunt the law in one instance, then it must be OK to do so in any instance, right?