Article 286 of Constitution of India "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 the sale or purchase of goods where
such sale or purchase takes place-
(a) outside the State; or
(b) in the course of the import of the goods into, or export
of the goods out of, the territory of India.
(2) Parliament may by law formulate principles for
determining when a sale or purchase of goods takes place in
any of the ways mentioned in clause (1).
(3) Any law of a State shall, in so far as it imposes, or
authorises the imposition of,-
(a) a tax on the sale or purchase of goods declared by
Parliament by law to be of special importance in inter-State
trade or commerce; or
(b) a tax on the sale or purchase of goods, being a tax of
the nature referred to in sub-clause (b), sub-clause (c) or
sub-clause (d) of clause 29-A of Article 366, be subject to
such restrictions and conditions in regard to the system of
levy, rates and other incidents of the tax as Parliament may
by law specify.
Article 287 of Constitution of India "Exemption from taxes on electricity"
Save in so far as Parliament may by law otherwise
provide, no law of a State shall impose, or authorise the
imposition of, a tax on the consumption or sale of
electricity (whether produced by a Government or other
persons) which is -
(a) consumed by the Government of India, or sold to the
Government of India for consumption by that Government; or
(b) consumed in the construction, maintenance or operation
of any railway by the Government of India or a railway
company operating that railway, or sold to that Government
or any such railway company for consumption in the
construction, maintenance or operation of any railway, and
any such law imposing, or authorising the imposition of, a
tax on the sale of electricity shall secure that the price
of electricity sold to the Government of India for
consumption by that Government, or to any such railway
company as aforesaid for consumption in the construction,
maintenance or operation of any railway, shall be less by
the amount of the tax than the price charged to other
consumers of a substantial quantity of electricity.