As per my understanding commencement of new business is governed by section 149(2A) of Companies Act, 1956. Penalty for non-compliance is given in section 149(6) which is as follows:
If any company commences business or exercises borrowing powers in contravention of this section (section 149), every person who is responsible for the contravention shall, without prejudice to any other liability, be punishable with fine which may extend to five thousand rupees for every day during which the contravention continues.
However section 149(7) is not applicable to a private company.
But if a private company plans to carry out any business not specified in Main object or other Objects, then it can not do so unless it follows the provisions of Section 17 & 18.
And non-compliance of Section 17 & 18 is penalised under Section 19 which says that such alteration shall be void.
Thus, a pvt. company can not enter into new b/s (not in its objects clause of MOA) without following Scetion 17 & 18.
It means whenever any amendment made in AoA & MoA , Date to make such amendment should be mentioned as Footnote. So that it can be easily identified that such & such clause /Provision was not exist in original memorandom. it was made latter and PRACTICALLY it also helps you to identify which MoAor AoA u have to followed because u have made new provision in ur Moa/Aoa but u have also old copy of such document in that case how will u easily identified which one contyain such provision.