Can a company change polices over serving Notice Period over-night ?

Hi, I am working in a Indian based company. While joining, in my offer letter it is mentioned that I have to serve 90 days of notice period. In case party does NOT serve the notice period then they shall be liable to pay basic salary and allowances in lieu of the notice period. But recently they changed the policy and mentioned that applicable to the existing policies and offer letter clauses as well. -No relaxation within 90 days of Notice period for an active employee and forthcoming employees. How this could be possible, there is no employee favor. Policy published on mid of night and mentioned that is effective from that time on wards. Can we raise voice against these points ?