It depends on your contract terms. If it is agreed in your contract with the company on the rules of how to take vacations, they can do as agreed or to reject your holiday application, otherwise you can argue with them, or seek Labour Department's advise.
Do you think your company is unfair to you? You can discuss with your company and try to come up with the reasonable procedures in applying for leaves.
Do not be afriad. Go ahead to talk and check with your Company. This is the rights of us, as employees.