N.Y. Civil Practice Law & Rules § 322
Rule 322. Authority for appearance of attorney in real property action. (a) Authority of plaintiff's attorney. Where the defendant in an action affecting real property has not been served with evidence of the authority of the plaintiff's attorney to begin the action, he may move at any time before answering for an order directing the production of such evidence. Any writing by the plaintiff or his agent requesting the attorney to begin the action or ratifying his conduct of the action on behalf of the plaintiff is prima facie evidence of the attorney's authority.