Millions of Americans are preparing to take time off from work for the holidays this month or next – and many of them are doing it without really knowing what employers legally can and can't do when it comes to vacation time.

Can your manager refuse to approve your time off? Do you have to be paid if your office shuts down for the holidays? What if your boss keeps contacting you with work questions while you're on vacation? Here are answers to all these questions and more.

[See: 8 Things You Really Need to Know About the Family and Medical Leave Act .]

Does your manager have to approve your time off?

Nope! Your manager is not required to agree to the specific days you request off. That said, good managers will try to accommodate you if at all possible, as long as you have the time saved up and the days you're requesting won't cause issues with work coverage. But it's good to be aware that your manager doesn't have to say yes, so that you can get your requests in early.

What if your manager never agrees to approve time off?

If your manager keeps turning down your requests for time off and you don't seem to ever be able to get away, try pointing out that your vacation time is part of your compensation and that you need to be able to use it. Say something like this: "I haven't been able to take time off in more than a year. That's not sustainable, and it's important to me to be able to use the benefits the company provides as part of compensation. Can we figure out how to arrange things so that I'm able to use my time off and get away to recharge?"

[See: 10 Things They Don't Tell You About Your First Job .]

Can your office contact you while you're on vacation?

Annoying as it may be, your office can indeed contact you with work questions while you're on vacation . If you're considered a "nonexempt" employee (you'll know you're nonexempt if you're eligible for overtime pay) and you're taking unpaid vacation time, they have to pay you for any time they take up while you're away. If you're taking paid vacation time, they don't have to pay you extra to make up for the time they took up.

That said, reasonable offices will let you warn people in advance that you'll be inaccessible while you're away. If you work in a less reasonable office, you can always mention that you'll be in a destination with poor cell phone coverage.

Can your employer have a use-it-or-lose-it policy for vacation time?

In most states, it's legal for employers to require you to use your vacation time by a certain date, usually the end of the year, or lose it altogether. However, California, Colorado, Nebraska and Montana prohibit use-it-or-lose-it policies. Employers in those states can cap how much vacation time employees are able to accrue (for example, saying that once you accrue 100 hours, you won't continue to accrue until you use some of it up), but once the time is accrued it can't be taken away.

[See: How to Quit Your Job Like a Class Act .]

If your company closes for the holidays, must you be paid for those days?

The answer to this depends on whether you're exempt or nonexempt, and how long your company closes for. If you're nonexempt, you're required to earn overtime pay when you work more than 40 hours in a week, but your employer can dock your pay when you work fewer hours. That means that if you're nonexempt and your company closes for a holiday, it's not required to pay you.

If you're exempt (not required to receive overtime pay), your company cannot dock your pay for office closings unless the closing lasts a full week or longer. However, you can be required to deduct the time from your leave balance, even though it wasn't your choice not to work those days.

Does your employer have to pay out the value of your remaining vacation time when you leave your job?

This depends 100 percent on what state you live in. Some states, including California, require your employer to pay you the value of any remaining vacation time when you leave, because they consider vacation time part of your wages. Other states leave it up to individual employers to decide. It pays to know your state law!

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