Retrospective sales tax levy cannot revive a lawful exemption without clear legislative authority.

A valid sales tax exemption cannot be converted into a retrospective tax liability merely because a later amending Act omits the exemption entry with retrospective effect. Where the exemption was in force throughout the relevant period, a deeming provision alone does not authorise past levy in the absence of an express legislative mandate. The operative principle is that lawful exemption during the taxable period defeats retrospective assessment unless the statute clearly creates such liability.

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Issues: Whether sales tax could be levied retrospectively for the period during which the petitioner had been validly exempted from tax, after the exemption was withdrawn by a subsequent amending Act.

Analysis: The exemption from sales tax had been granted under the principal Act and was in force throughout the period in dispute. The amending Act later omitted the relevant exemption entry with retrospective effect by a deeming provision, but it did not contain any express provision authorising retrospective levy of sales tax on persons who had already enjoyed a lawful exemption. A deeming clause could not be used to convert a lawfully enjoyed exemption into a past tax liability in the absence of a clear legislative mandate. Since the petitioner was exempt during the relevant period, the subsequent withdrawal of that exemption did not by itself create retrospective liability.

Conclusion: The retrospective levy of sales tax for the period in dispute was not valid, and the petitioner's challenge succeeded.

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