(1) A petition filed by employees or an employee organization must be accompanied by a showing of interest indicating that the petitioner has the support of at least 30 percent of the employees in the bargaining unit which the petitioner claims to be appropriate. The showing of interest must be filed under the same timeliness standards applicable to the petition and consist of original or legible paper or electronic copies of individual authorization cards or letters signed and dated by employees in the bargaining unit claimed appropriate. Authorization cards or letters are not valid unless signed and dated during the one-year period preceding the filing of the petition. The authorization cards submitted in support of a petition under this section must, at a minimum, contain the following:

(a) The employee's name typed or printed legibly, the employee's signature, and the date of the employee's signature;

(b) A statement that the employee designates the named labor organization as the employee's exclusive bargaining representative for purposes of collective bargaining;

(c) A statement that the showing of interest may be used for purposes of a card check election;

(d) A statement that the employee understands that the employee's signature on the card may be used to obtain certification of the named labor organization as the exclusive bargaining representative of the employee without a secret ballot election; and

(e) A statement that the employee has the right to ask the agency to revoke the employee's authorization card for purposes of card check.

(2) The agency shall notify the petitioner of the existence and number of any revocations filed under subsection (1)(e) of this section before the commencement of the card check but shall not disclose the identities of the employees involved.

(3) For any bargaining unit affected by RCW 74.39A.270 and 74.39A.300, the showing of interest requirement described in subsection (1) of this section is 10 percent for either a petitioner or an intervenor.

(4) The agency shall not disclose the identities of employees whose authorization cards or letters are filed with the agency in proceedings under this chapter.

(a) A petitioner or intervenor shall not serve its showing of interest on any other party to the proceeding.

(b) The question of whether a showing of interest requirement for a petition or for intervention has been satisfied is a matter for administrative determination by the agency and may not be litigated at any hearing.

(c) To preserve the confidentiality of the showing of interest and the right of employees to freely express their views on the selection of a bargaining representative, the agency shall not honor any attempt by an employee to withdraw any authorization submitted for purposes of this section.