(a) The mortgage may provide for the collection by the mortgagee of a late charge in accordance with terms, conditions, and standards of the Commissioner for each dollar of each payment to interest or principal:

(1) More than 10 days in arrears to cover the expense involved in handling delinquent payments;

(2) For multifamily project mortgages for which HUD issued a firm commitment for mortgage insurance before September 1, 2011, and for multifamily project mortgages insured under section 232 of the Act (12 U.S.C. 1715w), more than 15 days in arrears to cover the expense involved in handling delinquent payments.

(b) Late charges shall be separately charged to and collected from the mortgagor and shall not be deducted from any aggregate monthly payment.