While there are certainly insane laws and regulation in the US, I'm not sure I understand what would even possess a government to require such a thing. I mean, some companies even have paid sabbaticals even if they're not common. That certainly would seem like totally inappropriate meddling into company benefits for no good reason.

I'd understand (though not agree with) an individual company capping an individual vacation at three weeks, but not a (presumably) state law to that effect.