P. K. MISRA, J. - In order to appreciate the contentions raised on behalf of the parties, it is necessary to notice the relevant provisions in a historical perspective. Section 2(1)(a) of the Tamil Nadu Additional Sales Tax Act, 1970 as it stood prior to August 1, 1996, was to the following effect :

"Section 2. Levy of additional tax in the case of certain dealers. - (1)(a) The tax payable under the Tamil Nadu General Sales Tax Act, 1959 (Tamil Nadu Act 1 of 1959) (hereinafter in this section referred to as the said Act), shall, in the case of a dealer whose taxable turnover for a year exceeds ten lakhs of rupees, be increased by an additional tax calculated at the following rates, namely :

Rate of tax

(i) Where the taxable turnover exceeds ten 1.5 per cent of the lakhs of rupees, but does not exceed one taxable turnover crore of rupees :

Provided that no additional tax shall be payable under this item for the first ten lakhs of rupees of the taxable turnover.

(ii) Where the taxable turnover exceeds one 2 per cent of the crore of rupees but does not exceed five taxable turnover crores of rupees.

(iii) Where the taxable turnover exceeds five 2.25 per cent of the crores of rupees but does not exceed ten taxable turnover crores of rupees.

(iv) Where the taxable turnover exceeds ten 2.5 per cent of the crores of rupees but does not exceed taxable turnover three hundred crores of rupees.

(v) Where the taxable turnover exceeds 3 per cent of the three hundred crores of rupees. taxable turnover."

The aforesaid provision was amended by Act 31 of 1996 and in place of the expression dealer, the words "a casual trader or agent of a non-resident dealer or a local branch of a firm or company situate outside the State" was substituted. The amending Act also provided for insertion of clause (aa) after clause (a) to the following effect :

"2. Levy of additional tax in the case of certain dealers. - (1)(aa) The tax payable under the Tamil Nadu General Sales Tax Act, 1959 (Tamil Nadu Act 1 of 1959) (hereinafter in this section referred to as the said Act), shall, in the case of a dealer including the principal selling or buying goods in this State through agents other than a casual trader or agent of a non-resident dealer or a local branch of a firm or company situated outside the State whose taxable turnover for a year exceeds one hundred crores of rupees, be increased by an additional tax calculated at the following rates, namely :

Rate of tax

(i) Where the taxable turnover exceeds one 2.5 per cent of the hundred crores of rupees but does not taxable turnover. exceed three hundred crores of rupees.

(ii) Where the taxable turnover exceeds three 3 per cent of the hundred crores of rupees. taxable turnover.

Explanation. - 'Taxable turnover' for the purpose of this clause in respect of a principal selling or buying goods in this State through agents shall be the aggregate taxable turnover of all his agents relating to the sale or purchase of the goods of such principal within the State."

Such amendment came into force with effect from August 1, 1996. The net result of such amendment was to the effect that the registered dealers within the State were liable to pay additional sales tax only if their taxable turnover exceeded Rs. 100 crores, whereas, a casual trader and agent of a non-resident dealer and a local branch of a firm or company situated outside the State were liable to pay additional tax if their taxable turnover exceeded Rs. 10 lakhs. Of course the additional sales tax payable varied according to quantum of taxable turnover.

After such amendment was brought into force, the provisions were challenged before the Tamil Nadu Taxation Special Tribunal (Siemens Ltd. v. State of Tamil Nadu [1998] 110 STC 313 (TNTST)) on the footing that there was violation of articl