Question: Yesterday Indian parliament passed citizenship amendment bill which seeks to provide citizenship to religious minorities which have to come to India before Dec 2014 as a refugee due to their persecution in Pakistan, Bangladesh and Afghanistan.

I know it can be challenged in Supreme Court if the President of India signs it which he is most likely to do.

Today Kerala Chief Minister said that he would not allow it to be implemented in his state.

So does a state in India has power to stop implementation of a bill unilaterally?

Answer: 
India is a quasi-federation
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Powers are split between the state and national government as detailed in the [constitution](https://en.wikipedia.org/wiki/Constitution_of_India#Constitution_and_government). India is a halfway point between full federations (e.g. USA, Australia) and unitary nations (e.g. France, Austria) - it still has sovereign states like a federation but the national government has much more power to intervene.

Notwithstanding, citizenship is solely the province of the national government - Indian states have **no** power over it.
No. The bill was passed by the [national legislature](https://knowindia.gov.in/profile/the-union/legislature.php), and its laws will therefore be enforced by federal agencies, such as the [Bureau of Immigration](https://boi.gov.in). These agencies are controlled by the federal executive, the [Union Council of Ministers](https://en.wikisource.org/wiki/Constitution_of_India/Part_V#Article_74_.7BCouncil_of_Ministers_to_aid_and_advise_President.7D). In the case of the Bureau of Immigration, they would report to the Minister for Home Affairs.

In order for a *state* Chief Minister to "unilaterally" stop a *federal* bill from being implemented, that would imply some form of control over the Bureau of Immigration. **He does not have that power.**

However, as user6726 rightly points out, states may frustrate the implementation of the citizenship bill.