Pay the basic salary amount for those days to the company - if leaving early - Is that alright as per law?

Dear all, I am working in a so-called 100year old company. As per our appointment letter in the provisional period, there will be 1 month of notice period after conformation notice period will be 90 days. If any not possible to stay full period of notice then have to pay the basic salary amount for those days to the company. Then only the company will release you. Is that alright as per law? Last week they announced that the company will not take money from now. But everyone should have to complete the 90 days notice period.in this situation what should we do??

The settled position of law is that the employer has the right to insist on serving the full notice period or accept notice pay, partly or fully. So it is not objectionable for changing the rule. However, it would apply prospectively, so the Rule on the date of resignation would prevail.