unless such purchase is authorized by the vote of a majority of directors of the board or of a majority of a committee authorized by the board, provided that if such property would, upon purchase thereof, constitute all, or substantially all, of the assets of the corporation, then the vote of two-thirds of the entire board shall be required, or, if there are twenty-one or more directors, the vote of a majority of the entire board shall be sufficient.
N.Y. Not-For-Profit Corp. Law § 509