(1) A nonprofit organization or group of nonprofit organizations which is liable for reimbursement payments in lieu of contributions shall pay to the commission an amount equal to the full amount of regular benefits plus the amount of extended benefits and training benefits paid during any calendar quarter that is attributable to service in the employ of such organization and which is not reimbursable by the federal government. The amount which a nonprofit organization or group of nonprofit organizations is required to pay shall be ascertained by the commission as soon as practicable after the end of each calendar quarter and a statement of charges shall be mailed to each nonprofit organization or group of organizations. Payment of the amount indicated in the statement of charges shall not be made later than 30 days after the statement of charges was mailed.

    (2) Past due reimbursement payments in lieu of contributions shall be subject to the interest, penalty, assessment, and collection provisions provided in section 15.