Extending Notice Period through mail - increased my notice period from 2 to 3 months. Is this even legal?

Hi, I have given an offer letter in May 2020 with 2 months notice period. Now I got an opportunity where I need to join after 1.5 months So I am ready to pay for 15 days. But Management is saying they have sent out a mail on 1st march 2021 which has increased my notice period from 2 to 3 months. Is this even legal? They have not rolled out any letter or any other document. What should I do now?

The management can enforce any new rule only after informing the employees, particularly when it is in the amendment of the contract of service. You must respond to it by saying that as per the contract of service entered with you, the notice period is only 2 months and there cannot be any unilateral change in it. The so-called mail of 1st March, you should stress that it is an afterthought, a backdated document which has so far been not informed to you. Since the amended clause is detrimental to your interests it can only have a prospective effect, that is those resignations made after the issue of the communication unless the effective date is mentioned otherwise.