(1) As to whether an employing unit is an employer subject to this chapter, or
(2) That services performed by an individual for an employer liable for reimbursement payments in lieu of taxes is employment subject to this chapter,
shall become final 20 days after written notice of the determination is mailed to the last-known address of the employing unit of record with the director unless within such time the employing unit files an application with the director for a hearing with respect thereto as provided in ORS 657.683. [1963 c.354 §2 (657.552, 657.652, 657.679, 657.681 and 657.683 enacted in lieu of 657.472, 657.512, 657.550 and 657.672); 1975 c.156 §4; 1977 c.538 §11]