Every contract entered into by either of the two companies in relation to any of its undertakings which has vested in the Central Government under section 3 for any service, sale or supply, and in force immediately before the appointed day, shall, on and from the expiry of a period of thirty days from the appointed day, cease to have effect unless such contract is, before the expiry of that period, ratified, in writing, by the Central Government or the Government company concerned, in which such undertaking has been vested under this Act and in ratifying such contract, the Central Government or such Government company may make such alteration or modification therein as it may think fit:
     Provided that the Central Government or the such Government company shall not omit to ratify a contract and shall not make any alteration or modification in a contract--
         (a) unless it is satisfied that such contract is unduly onerous or has been entered into in bad faith or is detrimental to the interests of the Central Government or such Government company; and
         (b) except after giving the parties to the contract a reasonable opportunity of being heard and except after recording in writing its reasons for refusal to ratify the contract or for making any alteration or modification therein.