In general, an employee in Washington can be fired for no reason at all, provided that the termination is not based on discrimination, and the employee is not subject to an employment contract, a collective bargaining agreement, or other terms of employment providing for termination only for cause. This is called “at will employment,” meaning the employee can be terminated for any reason or no rason at all, and the employee can leave employment for any reason.
Assuming your husband was an “at will” employee, as most employees in Washington are, then he would not have a case for wrongful termination. However, if he had an employment contract or a collective bargaining agreement stating that he can only be terminated “for cause” or something of the like, then his potential claim for wrongful termination would be based upon the specific terms of his agreement with the employer.
For example, many employment contracts or collective bargaining agreements have provisions on progressive disclipline, investigating allegations against an employee, etc., which may govern in this particular situation. If your husband is subject to an employment contract, collective bargaining agreement, or believes he was fired due to discrimination based on a protected category (age, sex, religion, national origin, color, etc.), then he should speak to an attorney to provide more specifics of this potential claim.