Unless such a denial violates the terms of a union agreement or employment contract, it is legal. There is no automatic right to a raise. The fact is that most work relationships are "at will". This means that a business can set the conditions of work much as it sees fit (absent some form of legally actionable discrimination). That having been said, if you used PTO or a vacaton day to cover your absence you would need to be paid for the day that you take off.