Oregon is an at will employment state which means the employer can terminate your employment at any time for any reason or no reason provided it doesn't violate public policy or the law. If you are working in a non-union shop, and have not collective bargaining agreement, then you have no seniority rights. An employer is free assign employees at will to any position on any schedule, provided that he doesn't violate wage and hour laws for overtime.
It is an unfortunate situation for employees and doesn't necessarily represent good management, but it is not illegal.
Best of luck.
