The only real issue is whether or not you have a written employment contract. If you do, you can enforce it, and it may well protect your job--you need to review its terms (since contracts are enforced according to their terms) to see what protection, if any, if offers you.However, if you do not have any employment contract, you are an employee at will, and may be terminated at any time, for any reason, including that the employer has decided it wants all staff to have drivers licenses.