Moot Point: Delegation of Power under Article 14

Me and my friend have been arguing over this question and we can't seem to agree. It's from CLAT UG's past paper. Help us settle this!

Question: X, a public servant, is authorized by the State Legislature to impose taxes for local municipal purposes under Article 280 of the Constitution. Can X's decision of imposing a certain tax be challenged on the ground of discrimination under Article 14? Justify your answer.

Arguments:

My friend (let's call him Rohan) says: Yes, X's decision can be challenged as it amounts to legislative delegation of power in the form of a general authority to impose taxes. This is a clear case of legislative delegation which is ultra vires.

I say: No, X's decision can't be challenged.