You can read the summaries of Labor & Industries' position on scheduling here: http://www.lni.wa.gov/WorkplaceRights/Wages/HoursBreaks/Hours/default.asp .
Most employers in WA are regulated by L&I. Your employer likely is regulated by L&I.
If you are in a union or has a direct contract with the employer, the union or your contract may have provisions about scheduling.
It is likely an extremely poor business practice to change employee's schedules without notice. However, the law often does not penalize poor business practices that do not affect public's safety.
You can check whether the change in schedule without notice is a way to find a cause to fire you. In WA employment is generally at will, meaning that an employer does not need a cause to fire an employee as long as the firing is not in violation of specific statutes. To lessen the risk of losing a claim of unlawful firing, businesses sometimes will set an employee up to show that there is an apparent cause to fire the employee.
If you believe what your employer is doing is unlawful, you can review your specific facts with your attorney to see what your legal options are.Ask a similar question