In order to improve constraint satisfaction techniques, a promising way is to use special features of constraints and variable domains. This paper examines a special class of CSPs (Constraint Satisfaction Problems) in which a partial order is defined on each domain and the constraints are compatible with these orders. A special arc-consistency algorithm for this case is presented and some questions about finding all solutions are discussed. The presented ideas can be used in constraint systems implemented in an object-oriented language, where inheritance hierarchy of objects is a natural support for the presented CSP type.