N.Y. Business Corporation Law § 609
(f) A proxy which is entitled "irrevocable proxy" and which states that it is irrevocable, is irrevocable when it is held by any of the following or a nominee of any of the following:
(i) Without limiting the manner in which a shareholder may authorize another person or persons to act for him as proxy pursuant to paragraph (a) of this section, the following shall constitute a valid means by which a shareholder may grant such authority.