In our recent appraisal cycle, our company changed the terms of employment without prior discussions. We now have to serve a 2 months notice period, which earlier was 1 month as per the original appointment letter. Also, they have advised that in case we quit this job within 12 months of this new terms coming into affect, we would have to pay back the hike money (change in compensation) that was paid to us since.

Can someone please advice if this is legal? I mean I joined this company accepting the terms and conditions which were mentioned in the appointment letter at that time. How can employer change the terms suddenly?

Please help.