New York Codes, Rules and Regulations
Title 20 - DEPARTMENT OF TAXATION AND FINANCE
Chapter IV - Sales And Use And Other Miscellaneous Taxes
Subchapter D - Mortgage Recording Taxes
Part 647 - Credit Line Mortgage
Section 647.2 - Effect of increasing the maximum principal amount secured by a credit line mortgage

Tax Law, § 253-b

If the maximum principal amount upon which the taxes computed pursuant to section 647.1 of this Part is increased, further taxes are payable at the time an instrument evidencing such increase is recorded. Such further taxes shall be computed in accordance with the provisions of section 647.1 of this Part but only upon the amount of such increase in maximum principal amount plus the amount of any new funds, if any, as defined in section 641.9 of this Title.