N.Y. Comp. Codes R. & Regs. tit. 8 § 400.2
Every employee to whom this procedure applies shall have the right to present his grievance in accordance with this procedure, free from interference, coercion, restraint, discrimination or reprisal. Every employee shall have the right to present his grievance personally, or to be represented by a person of his own choosing at all steps of this procedure, except that where there is in effect a collective agreement covering a negotiation unit which includes such employee, which was entered into between the State and an employee organization, then such employee may not choose as his representative, any employee organization other than the organization with which such agreement was negotiated, nor may any employee organization other than the one with which such agreement was negotiated initiate or process a grievance except to the extent permitted by such agreements.
N.Y. Comp. Codes R. & Regs. Tit. 8 § 400.2