Nowadays, business processes have become an ubiquitous part in public institutions, and the success of an e-government system depends largely on their effectiveness. However, despite the large number of techniques and technologies that are successfully used in the private sector, these cannot be transferred directly to public institutions without taking into account the strongly hierarchical nature and the rigorous legal basis on which public processes are based. This work presents an approach allowing the consideration of the legal requirements during the public processes design. Its main particularity is that these requirements are encapsulated using a legal features model supporting a formal semantic. This one prevents the violation of legal requirements and ensures that the processes evolution will in compliance with them.