Modeling for software development has been traditionally made by CASE tools. In these tools, formalisms for every model are completely defined, which implies it’s not possible adding new restrictions. Meta-modeling tools emerge like a solution for this problem, because they have their own formalisms (generally in graphic environment) allowing different model expressions, including restrictions. In this paper a proposal for involving restrictions in UML class model using AToM 3 (a meta-modeling tool) has been presented.