New York Laws
Part 4 - Liability of Parties
3-406 - Negligence Contributing to Alteration or Unauthorized Signature.


Signature.

Any person who by his negligence substantially contributes to a
material alteration of the instrument or to the making of an
unauthorized signature is precluded from asserting the alteration or
lack of authority against a holder in due course or against a drawee or
other payor who pays the instrument in good faith and in accordance with
the reasonable commercial standards of the drawee's or payor's business.