I can’t speak to other states, but this is legal in California. It’s also worth noting that employers are required to pay final wages — including unused PTO —

I can’t speak to other states, but this is legal in California. It’s also worth noting that employers are required to pay final wages — including unused PTO — within 72-hours of your final final shift. So, the power move in response to such an employer would be to say you are quitting effective immediately and you expect your final check, including unused PTO, to be mailed out within 72-hours. “Fuck me? No, fuck you.”