(1) The department shall investigate a complaint filed by an interested party unless the complaint was filed more than thirty days after the date the public agency accepted the public work that gave rise to the complaint. The department may, in its sole discretion, investigate a complaint filed more than thirty days after the acceptance date. However, the department may not charge a contractor with a violation of RCW 39.12.065 if the complaint is filed after the thirty-day limit.

The department's investigation shall determine whether a violation of RCW 39.12.065 or 39.12.050, or both, or of any other provision of chapter 39.12 RCW, occurred.

(2) If the department's investigation substantiates a complaint that alleges that a contractor has violated RCW 39.12.065, the department is required to attempt to collect unpaid wages for the contractor's employees. During the investigation, the department should be able to identify the affected employees. The department shall direct to the affected employees the best notice practicable under the circumstances, including individual notice to all employees who can be identified through reasonable effort. The notice shall inform the employee that (a) the department's final order, whether favorable or not, will apply to all employees; (b) any employee may, if he or she desires, move to intervene as a party in any hearing held as a result of the investigation; and (c) that the employee may have a private right of action to collect unpaid prevailing wages.