In order to be acceptable as evidence of representation for the purposes of the thirty percent requirements of section 3 of the act, individual authorization cards must be signed and dated by the employee expressing his intention to be represented by a specific bargaining representative. A card signed and dated six months or more prior to the date on which examination of cards for representation purposes commences shall be considered invalid and not acceptable for representation purposes.
Wash. Admin. Code § 296-133-190
Order 72-13, § 296-133-190, filed 7/31/72.