Section 253-B - Credit line mortgage1. In the case of a mortgage which is a credit line mortgage, as defined in subdivision two of this section, of real property principally improved or to be improved by a one to six family owner-occupied residence or dwelling, the principal debt or obligation which is or under any contingency may be secured at the date of execution of such mortgage or at any time thereafter within the meaning of this article shall mean the maximum principal amount specified in such mortgage. If the tax imposed by and pursuant to the authority of this article is paid on such maximum principal amount, no further tax shall be payable on advances or readvances by the lender pursuant to the recorded primary mortgage, provided such advances or readvances are made to the original obligor or obligors named in such recorded primary mortgage. In the event the maximum principal amount of a credit line mortgage is increased, a tax is imposed as provided in section two hundred fifty-three and pursuant to the authority of section two hundred fifty-three-a of this article on such new or further indebtedness or obligation when the instrument evidencing such further indebtedness is recorded. In order to better enforce the provisions of this subdivision and for the privilege of recording an instrument evidencing a sale or transfer of real property on which the lien of a credit line mortgage remains outstanding, in the event that a credit line mortgage remains outstanding after the sale or transfer of the real property securing the credit line mortgage to a person or persons who is or are not related to the original obligor or obligors by blood, marriage or adoption, or where such credit line mortgage that remains outstanding after such sale or transfer is a credit line mortgage of property other than real property principally improved or to be improved by a one to six family owner-occupied residence or dwelling, taxes are imposed at the rates applicable under section two hundred fifty-three and pursuant to the authority of section two hundred fifty-three-a on the principal debt or obligation which is or under any contingency may be secured at the date when the instrument evidencing the sale or transfer is recorded and no such instrument shall be recorded until the taxes imposed in this section are paid.1-a. In the case of a mortgage which is a credit line mortgage, as defined in subdivision two of this section, of property other than real property principally improved or to be improved by a one to six family owner-occupied residence or dwelling, and where such mortgage is of an amount less than three million dollars, the tax imposed by and pursuant to the authority of this article shall be imposed and paid pursuant to the provisions of subdivision one of this section.2. For the purposes of this section, a "credit line mortgage" shall mean any mortgage or deed of trust, other than a mortgage or deed of trust made pursuant to a building loan contract as defined in subdivision thirteen of section two of the lien law, which states that it secures indebtedness under a note, credit agreement or other financing agreement that reflects the fact that the parties reasonably contemplate entering into a series of advances, or advances, payments and readvances, and that limits the aggregate amount at any time outstanding to a maximum amount specified in such mortgage or deed of trust. For the purpose of this section, "credit line mortgage" shall not include a reverse mortgage as defined in sections two hundred eighty and two hundred eighty-a of the real property law.3. The commissioner shall promulgate regulations to provide for the enforcement and administration of the taxes imposed by or pursuant to subdivisions one and one-a of this section.