With the US is it the vacation rules are mostly not required. Many states have different rules, and the more conservative the state, the more anti worker the rules are.
And all the jobs I've worked, I've never seen any pushback for taking vacation. But that's because I work in a white collar industry that is competitive and I can find another job if I wanted to. The less skilled you are, and the lower the opportunities are in the industries around you, the more opportunity exists for shitty employers.
The interesting thing is, that I currently work for a Scottish company, and their vacation rules are worse than mine because I am guided by California labor laws, and they're under shitty UK labor laws.