N.Y. GOB Law § 5-301

§ 5-301. Certain employment contracts void. Every undertaking or\npromise, whether written or oral, express or implied, constituting or\ncontained, in any contract or agreement of hiring or employment between\nany individual, firm, company, association or corporation and any\nemployee or prospective employee of the same, whereby (a) any employee\nor prospective employee undertakes or promises to join, become or remain\na member of a company union; or (b) either party to such contract or\nagreement undertakes or promises not to join, become, or remain a member\nof any labor organization or any organization of employers; or (c)\neither party to such contract or agreement undertakes or promises that\nhe will withdraw from the employment relation in the event that he\njoins, becomes or remains a member of any labor organization or of any\norganization of employers, is hereby declared to be contrary to public\npolicy and wholly void and shall not afford any basis for the granting\nof legal or equitable relief by any court against a party to such\nundertaking or promise, or against any other persons who may advise,\nurge or induce, without fraud, violence, or threat thereof, either party\nthereto to act in disregard of such undertaking or promise.\n