Common law protects an employee from retaliation if the employee disobeys an employer on the grounds that the employer ordered him or her to do something illegal or immoral. However, in the majority of cases, the burden of proof remains upon the discharged employee. No U.S. state but Montana has chosen to statutorily modify the employment at-will rule. In 1987, the Montana legislature passed the Wrongful Discharge from Employment Act (WDEA). The WDEA is unique in that, although it purports to preserve the at-will concept in employment law, it also expressly enumerates the legal bases for a wrongful discharge action. Under the WDEA, a discharge is wrongful only if: "it was in retaliation for the employee's refusal to violate public policy or for reporting a violation of public policy; the discharge was not for good cause and the employee had completed the employer's probationary period of employment; or the employer violated the express provisions of its own written personnel policy."