New York Domestic Relations Law Section 5 - Incestuous and void marriages.

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

Last modified: February 3, 2019