In the instant case, we are concerned with the taxation of goods which under s. 14 of the Central Sales Tax Act have been declared to be of special importance in inter-State trade or commerce. Where the turnover of such goods is subjected to tax under the sales tax law of a State, s. 15 prescribes the maximum rate at which such tax may be imposed and requires that such tax shall not be levied at more than one point. The two conditions have been imposed in order to ensure that inter-State trade or commerce in such goods is not hampered by heavy taxation within the State occasioned by an excessive rate of tax or by multipoint taxation. Section 15 enacts restrictions and conditions which are essential to the validity of an impost by the State on such goods. If either of the two conditions are not satisfied, the impost will be invalid. Now, in order that tax should not be levied at more than one stage, it is imperative that the sales tax law of the State should specify either expressly or by necessary implication the single point at which the tax may be levied. Alternatively, it may empower a statutory authority to prescribe such single point for the purpose. Where such point is not prescribed, either by the statute or by the statutory delegate, no compliance is possible with s. 15. The single point at which the tax may be imposed must be a definite ascertainable point so that both the dealer and the sales tax authorities may know clearly
