Section 48 talks about the variation of shareholder rights of particular class(s) of shareholders. It provides that if any company wants to vary the shareholder rights as comparison to originally issued rights, company is recquired to pass special resolution by postal ballot OR the consent of 75% of shareholder of such class(s) in writing. Provided
Such power is given in the AOA, if not given then not expressly prohibited as per the terms of issue at the time of originally issuance of such class(s) of shareholders
However if 10% of such class(s) didn't give their consent or didn't favor special resolution, they may apply for cancelling the such variation to NCLT.
(if 16% or more shareholder abstained themselves from voting variation is possible )