Paragraph (g) of subdivision (2) of section 3 of chapter 32 of the General Laws, is hereby amended by inserting after line 326 the following new paragraph:-

Any municipality or public authority may elect to improve the retirement group classification for any group of employees of the municipality or the public authority upon its acceptance in the following manner: in a city having a Plan D or a Plan E charter by majority vote of its city council and approved by the manager; in any other city by majority vote of the city council and approved by the mayor; in a town by vote of the board of selectmen; in a public authority by majority vote of the authority governing board. Nothing in this act shall be construed as authorization to diminish the retirement benefits of public employees by placing any group of employees in a lower group of classification.