When any employer fails to pay any contributions or payments required under this chapter the Commissioner shall make an assessment of contributions against such employer together with interest and penalty thereon. After making the assessment, due notice shall be given thereof, by ordinary or certified mail, to the employer and the assessment shall be final unless the employer petitions for a hearing on such assessment within the time hereinafter specified. (Amended 1961, No. 210, § 7, eff. July 11, 1961; 1989, No. 8, § 1; 1989, No. 8, § 1; 1991, No. 82, § 2.)