N.J. Stat. Ann. § 34:12-2

No corporation doing business in this state shall, directly or indirectly, require, as a condition of employment of labor in any branch of its service, that any applicants for employment shall, either individually or collectively, be required to sign any paper, document, or writing of any description, by which an obligation is made or implied of renouncing existing membership in an organization, society or brotherhood, or by which a promise is given of not joining such organization at any future time.