Evidence of representation or legitimate interest may be either individual authorization cards, membership records, or petition. In any case, the petition, membership records, or authorization cards must show the address and be signed and dated by the employee expressing an intent to be represented by a specific bargaining agent. Cards shall be considered valid if the dates thereon, and other evidence provided to the Board, indicate a regularity of continuing interest by the employees signing the petition or authorization cards. Such evidence of interest shall be presumed if the cards or other evidence of interest are signed within 180 days of the filing date.
Okla. Admin. Code § 585:35-3-3