Article 246A – Special Provision with Respect to Goods and Services Tax.

(1) Notwithstanding anything contained in articles 246 and 254, Parliament, and, subject to clause (2), the Legislature of every State, have power to make laws with respect to goods and services tax imposed by the Union or by such State.

(2) Parliament has exclusive power to make laws with respect to goods and services tax where the supply of goods, or of services, or both takes place in the course of inter-State trade or commerce.

Explanation.—
The provisions of this article, shall, in respect of goods and services tax referred to in clause (5), of article 279A, take effect from the date recommended by the Goods and Services Tax Council.’’.

Reference of Article 246 & Article 254

Article 246
Subject matter of laws made by Parliament and by the Legislatures of States (In Brief)

Parliament has exclusive power to make laws with respect to any of the matters enumerated in List I in the Seventh Schedule (in this Constitution referred to as the Union List)

The Legislature of any State also, have power to make laws with respect to any of the matters enumerated in List III in the Seventh Schedule (in this Constitution referred to as the Concurrent List)

Parliament has power to make laws with respect to any matter for any part of the territory of India not included (in a State) notwithstanding that such matter is a matter enumerated in the State List

Article 254
Inconsistency between laws made by Parliament and laws made by the Legislatures of States (In Brief)

(1)If any provision of a law made by the Legislature of a State is repugnant to any provision of a law made by Parliament which Parliament is competent to enact, or to any provision of an existing law with respect to one of the matters enumerated in the Concurrent List, then, subject to the provisions of clause ( 2 ), the law made by Parliament, whether passed before or after the law made by the Legislature of such State, or, as the case may be, the existing law, shall prevail and the law made by the Legislature of the State shall, to the extent of the repugnancy, be void

(2)Where a law made by the Legislature of a State with respect to one of the matters enumerated in the concurrent List contains any provision repugnant to the provisions of an earlier law made by Parliament or an existing law with respect to that matter, then, the law so made by the Legislature of such State shall, if it has been reserved for the consideration of the President and has received his assent, prevail in that State: Provided that nothing in this clause shall prevent Parliament from enacting at any time any law with respect to the same matter including a law adding to, amending, varying or repealing the law so made by the Legislature of the State