Union Government
When a Bill has been passed by the Houses of Parliament, it shall be presented to the President, who shall declare either assent or withholding of assent - provided that, for a non-Money Bill, the President may first return it (once) with a message asking the Houses to reconsider it or specific provisions; if the Houses pass it again, with or without amendment, and present it again, the President shall not withhold assent.
Once both Houses pass a Bill, it goes to the President, who can either give assent (making it law) or, for a non-Money Bill only, send it back once asking Parliament to reconsider. But if Parliament passes the same Bill again after reconsideration, the President is constitutionally required to give assent the second time - there is no absolute veto, only a one-time "return for reconsideration" power.
This is why the President cannot permanently block a Bill Parliament is determined to pass: if Parliament re-passes a returned Bill unchanged, the President has no further choice but to give assent to it.