The NRC does this...and it is part of the exercise by the government.
The NRC is just a register of citizens and that doesn't strip anyone from citizenship either. The exercise is meant to purge non-citizens from Indian registry of citizens, which really isn't controversial by itself.
The problem is that a significant number of people - some two million - live in India, were born in India, have no other country but India, but wouldn't be eligeble for Indian citizenship under these laws. These people already are stateless, India would simply not recognize their right to citizenship. India is of course technically allowed to do so, but it is unconscionable to reject citizenship to people who lived their entire lives in your country and have no other place to call home.
Note, I don't actually support the reform - it's unconscionable - but not for the reasons presented.
McHrozni