Companies Act, 1956
Sec 106 - Alteration of rights of holders of special classes of shares
Where the share capital of a company is divided into different classes of shares, the rights attached to the shares of any class may be varied with the consent in writing of the holders of not less than three-fourths of the issued shares of that class or with the sanction of a special resolution passed at a separate meeting of the holders of the issued shares of that class :
(a) if provision with respect to such variation is contained in the memorandum or articles of the company, or
(b) in the absence of any such provision in the memorandum or articles, if such variation is not prohibited by the terms of issue of the shares of that class.