Wash. Admin. Code § 357-19-090
Employers must publish a policy on probationary and trial service periods that minimally addresses the employer's basis for determining and notifying an employee:
[Statutory Authority: Chapter 41.06 RCW. WSR 05-19-009, § 357-19-090, filed 9/8/05, effective 10/10/05; WSR 05-01-206, § 357-19-090, filed 12/21/04, effective 7/1/05.]