Section 13 is hereby amended to read as follows: "SEC. 13. Retirement Option.
Section 4
SEC. 4. Section 13 is hereby amended to read as follows: "SEC. 13. Retirement Option. — Employees who are in the government service upon the affectivity of this Act shall, at the time of their retirement, have the option to retire under this Act or under Commonwealth Act No. 186, as amended, and their benefits and entitlement thereto shall be determine in accordance with the provisions of the law so opted: Provided, however, That in the event of his re-employment, his subsequent retirement shall be governed by the provisions of this Act: Provided, further, That the member may change the mode of his retirement within on year from the date of his retirement in accordance with such rules and regulations as may be prescribed by the System."