With the exception of certain California laws restricting laying off some janitorial and building service personnel and other displaced workers, no law dictates how you select workers for layoff.1
However, the process that you use to select whom you will lay off is subject to review as a result of federal and state laws that protect employees from unlawful discrimination and retaliation. An employee who believes that he/she was selected for layoff because of membership in a protected class or participation in a protected activity can file a claim against the company under state and/or federal anti-discrimination statutes.
Lab. Code secs. 1060-1065