Different exemptions to different categories or classes permissible :
It is permissible to grant different exemptions to different classes, as long as all those within a particular class are treated equally and uniformly. Statute can be declared invalid only when it is shown that the impugned statute is based on discrimination and that such discrimination is not referable to any classification which is rational and which has nexus with the object intended to be achieved by the Statute.
Thus, granting exemption to small scale units, or to units manufacturing goods without aid of power, or to undertakings or to a class of consumers will be permissible. However, such classification should be in public interest and powers should be used bona fide.
It is well recognised that State enjoys the widest latitude where measures of economic regulations are concerned. State can pick and choose districts, objects, persons, methods and even rate for taxation if it does so reasonably.