It is a little more nuanced than that. Many states have laws that say PTO is earned, it needs to be paid out 100% of the time, some say it depends on the written company policy, other say it never needs to be paid out. And similarly, Montana requires good cause to fire employees(except if they are new employees or meet a number of other exceptions), a number of states have exceptions to at-will that require employers to follow their own policies(and many large companies require two weeks notice, and good cause for firing) and a number have few to no exceptions to at-will.