286. Restrictions as to imposition of tax on the sale or purchase of goods.—(1) No law of a State shall impose, or authorise the imposition of, a tax on 1[the supply of goods or of services or both, where such supply takes place]—
(a) outside the State; or
(b) in the course of the import of the 2[goods or services or both] into, or export of the 2[goods or services or both] out of, the territory of India. 3[* * * *] 4[(2) Parliament may by law formulate principles for determining when a 5[supply of goods or of services or both] in any of the ways mentioned in clause (1). 6[(3) * * * *]