The States Reorganisation Act,1956
Section 26. Term of office of members
In order that, as nearly as may be, one-third of the members may retire on the 2nd day of April,1958, and on the expiration of every second year thereafter, the President shall, after consultation with the Election Commission, make by order such provisions as he thinks fit in regard to the terms of office of the members elected under section 25 and such modifications as he thinks fit in the terms of office of any of the sitting members.