WA is an "at will" state. Businesses may fire "at will." There are no laws regarding dismissal, so businesses are not required to give warnings or follow any particular steps.
That all seems to be a non-sequitur, since industrial action does not require that the event it is in response to is illegal (indeed, industrial action has frequently been directed against employers whose actions are not merely legal but strongly backed by government and supported with government force.)
Source: http://www.lni.wa.gov/WorkplaceRights/ComplainDiscrim/Termin...