1) If you took legally protected sick leave, like leave under the Family and Medical Leave Act (FMLA), you may not be retaliated against for using the leave--though you may have hours changed or reduced for other legitimate reasons, such as changes in the amount or scheduling of work. If you took FMLA leave and feel you have been retaliated against, you should speak with an employment lawyer about the specifics of your case, to see if you have a claim and what it might be worth.2) Note, however, that if you did not use leave, like FMLA leave, guaranteed by law, but rather took leave that your employer voluntarily choose to allow you, you have no such protection--the employer may now reduce your hours.3) As to the contract--the contract is enforceable as per its terms. If the contract would allow a reduction in your hours, then that is legal. You need to reference the specific terms of the contract to see what is and is not legal; if in doubt, an attorney can review the contract for you, to help you understand your rights.4) If you are not protected by a contract or by a medical leave law (like FMLA), your employer could give your job to another.