N.Y. Dom. Rel. Law § 5

§ 5. Incestuous and void marriages. A marriage is incestuous and void\nwhether the relatives are legitimate or illegitimate between either:\n 1. An ancestor and a descendant;\n 2. A brother and sister of either the whole or the half blood;\n 3. An uncle and niece or an aunt and nephew.\n If a marriage prohibited by the foregoing provisions of this section\nbe solemnized it shall be void, and the parties thereto shall each be\nfined not less than fifty nor more than one hundred dollars and may, in\nthe discretion of the court in addition to said fine, be imprisoned for\na term not exceeding six months. Any person who shall knowingly and\nwilfully solemnize such marriage, or procure or aid in the solemnization\nof the same, shall be deemed guilty of a misdemeanor and shall be fined\nor imprisoned in like manner.\n