There is no law in regards to vacation policy: it is up to each company to create any vacation policy it wants, and it may freely change this policy going forward on notice, from the moment it gives notice onward (unless that is, an employee has a contract setting his/her vacation; then the company must honor the contract). Companies can have no vacation, unlimited vacation, or anything in between, and are not locked into their initial policy forever; as stated, it is subject to change.