I'm pretty sure that's illegal. Report your boss to the HR, although that may be unnecessary as, according to your username, he will be dead

It's not illegal -- it's just shitty.

The boss's most capricious whims take priority over the subordinate's crises. Yay, capitalism!

Actually, if OP were to file for FMLA leave, it's illegal for their boss to not give it and to retaliate for it in any way.

If the leave was approved OP can safely ignore his boss and go unless there is some sort of emergency. His boss might try to fire him for some made up other reason but you can't fire or punish someone for taking their approved leave.

FMLA doesn't apply to small businesses or businesses of a protected class. The protected class is Trump donors and this is another way America is becoming great again.

No. I would have flat out refused. Let your boss explain to HR (and any labor board) why his spontaneous vacation to the Caribbean was more important than approved medical leave.
File a grievance. Immediately. And then take your pre-approved time off. Your boss can fucking suck it.

Report him to HR and take your vacation. If he still decides to take his during your vaction time, then report him again. You deserve to see your father.

Do not ALLOW this to happen to you. Don't let this asshole win. Take it to HR, threaten to quit your job, give him a piece of your mind, do whatever you may have to, but stand your ground. You will never forgive yourself if you don't go with your dad. I know I wouldn't even care about my job at that point. Your boss is a piece of shit. He will just keep doing this kind of crap. He can't just reschedule? What a dick.

It's unfair I think

oh hell no i would have called HR about that cuz that is extremely illegal

who the hell would hit the "you deserved it" button when u wanted the time off as ur dad was in hospice ? thats just mean and cruel! #yourbossisanass

I would quit and sue

Your job is never more important that your dad's life. Don't go to work. Be with your father. We only have one life, and it's short, we need to make the right decision in these situations. Which is to screw your job and your asshole boss and go be with your family.

That's a lovely sentiment, but for some people losing their job means homelessness or starvation for them and their family. Not everyone has savings for cases like this. Not everyone can afford it.

And her job may be helping to pay for her dad's care.