This is also illegal in Mexico: Your contract must say the number of vacation days you have, particularly because at the end of every year you get a "vacation bonus" (prima vacacional) that is proportional to your total yearly vacation days (25% or 50% pay of each day). If you don't use it, they still have to pay you. Of course if someone put that they give ∞ vacation days, the amount to pay yearly to each employee will be quit a bit haha.