(a) Any new employer or employer who was not insured at the end of the previous year shall file a statement on forms to be provided by the Commissioner of Finance including the estimated wages to be paid his workmen and shall pay the portion of the annual premium due on such wages to the Commissioner of Finance before commencement of work.
(b) Should any employer substantially increase his payroll during the term of insurance, he shall file a supplementary statement and pay the additional premiums based thereupon within 30 days after such increase.
(c) Any employer who prior to July 1 or January 1 of any year ceases to be subject to the provisions of this chapter may be excused from payment of premiums by giving notice and such proof required by the Commissioner of Finance.