Technically, probably not. We work off a point system, you earn so many for tardiness or unexcused absences and I'm sure they'd figure out a way to point someone for leaving unexcused on a supposed "normal work day" when that person agreed that they would be here (not that it seemed that person had a choice.)
As far as New Year's, I'm going to definitely do something. I'm one of the most dedicated and reliable employees in their eyes and at least in the top 4 of people they need to stay every day & Saturdays so if they maintain that NYE is even the possibility of "mandatory" then I'll just tell them I'm not staying and killing myself all of the other days until then. Then as it gets closer I'll probably email my HR to tell me if it actually is mandatory or if i'll get marked.
The thing is, a lot of people actually said they'd come in today if given the option. But as soon as everything played out, it completely changes your outlook. Like, you don't have to lie and threaten us to do it if you already had us on your side. Now they've pissed everyone off.