Section 10D. The commission shall establish a plan of disability insurance on such terms and conditions as it deems to be in the best interest of the commonwealth and its employees. With respect to any disability insurance which is in effect for an employee there shall be withheld from the salary or wages of such employee the premium for such insurance and the commonwealth shall make no contribution to said premium. The group insurance commission is hereby authorized to implement a system whereby such employee contributions are made on a pre-tax basis.