Supply of goods and/or services. CGST & SGST will be levied on intra-state supplies while IGST will be levied on inter-state supplies. The charging section is section 7 (1) of CGST/SGST Act and Section 4(1) of the IGST Act.
Article 246A of the Constitution, which was introduced by the Constitution (101st Amendment) Act, 2016 confers concurrent powers to both parliament and state legislatures to make laws with respect to GST. However, -clause 2 of Article 246A read with Article 269A provides exclusive power to the Parliament to legislate with respect to inter-state trade or commerce.