This already happens all the time for salaried employees, they often receive vacation time that doesn't reduce their yearly salary and this works perfectly fine for those roles. This isn't a tax scenario, this is more of a compensation adjustment for workers.
Vacation is still an option for employers, not a requirement. If the government required vacation time and a company did not previously offer vacation time, it's net-effect would still be an additional tax.
I'm not making a moral argument here -- actually find it rather immoral for a company not to offer adequate time off. I'm just saying the net-effect of a government forcing a company to pay more money than it normally would is a tax.
