N.Y. Pers. Prop. Law § 421

§ 421. Security interest in other property. Except as provided in\nsection four hundred ten of this chapter, no retail instalment contract\nor obligation, or any other agreement executed in connection therewith,\nmay provide for the creation of a security interest in any real or\npersonal property, other than the goods which are the subject matter of\nthe retail instalment sale, to secure the payment of the time sale price\nunder such contract or obligation or any part thereof; provided,\nhowever, that the prohibition of this section shall not be applicable to\nthe taking of a mortgage upon real property to secure the payment of the\ntime sale price of a retail instalment obligation, if the transaction\nwhich gave rise to such obligation was the furnishing of goods or\nservices for repairs, alterations or improvements upon, or in connection\nwith buildings upon, such real property. Any such prohibited provision\nshall be void but shall not otherwise affect the validity of the\ncontract or obligation.\n