If it was an enforceable employment contract, requiring the employee to work significantly more hours may well be a material breach entitling him or her to sue for compensation due to the breach (or allowing him or her to treat the contract as terminated). The key issue is: is it an enforceable contract. To be enforceable, not only must its terms be definite and unequivocal, and both employer and employee must have signaled their agreement to it, but it must be for a definite time or period (e.g, a one-year, two-year, etc. agreement). A "contract" which does actually lock in the terms of employment for a definite time is not actually enforceable, since without defining a period during which the terms may not be changed, they can be changed at any time.