N.Y. Lab. Law § 704-A
It shall not be an unfair labor practice for an employer engaged in the performing arts to make an agreement with a labor organization, of which performing artists are members, covering employees engaged in the performing arts, or who, upon their employment, will be so engaged, because the majority status of such labor organization has not been established under the provisions of this article or because such agreement requires, as a condition of employment, membership in such labor organization after the seventh day following the beginning of such employment or the effective date of such agreement, whichever is later. Nothing in this section shall be construed as to bar any proceeding brought pursuant to section seven hundred five of this article.
N.Y. Lab. Law § 704-A