BHAGWATI, J. - This petition under Article 226 of the Constitution raises a question relating to the construction of section 12A(4) of the Bombay Sales Tax Act, 1946, and in the event of the construction contended for on behalf of the State being accepted, challenges the vires of the section on the ground of lack of legislative competence on the part of the State to enact it. In order to appreciate the questions arising in the petition it is necessary to set out briefly the facts giving rise to the petition it is necessary to set out briefly the facts giving rise to the petition. The facts are few and for the most part undisputed and may be briefly stated as follows :-

The petitioners are dealers carrying on business in cloth and at all material times they held a certificate of registration under the Bombay Sales Tax Act, 1946 (hereinafter referred to as the Act). During the period 1st January, 1950, to 31st March, 1951, the petitioners effected various sales outside the State of Bombay. Those sales being outside State sales were exempt from tax by reason of Article 286(1) of the Constitution but in the mistaken belief that they were taxable the petitioners initially paid a sum of Rs. 17,786-2-9 as tax in respect of such sales. The petitioners thereafter realising that these sales were not taxable, made an application for refund of the sum of Rs. 7,788-2-9 on 15th May, 1953. The Sales Tax Officer assessing the petitioners to sales tax accepted the claim of the petitioners to the extent of Rs. 10,361-5-6 and by an order dated 19th June, 1956, granted refund of the sum of Rs. 10,361-5-6 to the petitioners. Pursuant to this order of the Sales Tax Officer a refund order dated 26th July, 1956, for Rs. 10,361-5-6 was issued in favour of the petitioners and the petitioners obtained payment of the said amount. Since the relief granted by the Sales Tax Officer was only a partial relief, the petitioners preferred an appeal to the Assistant Collector of Sales Tax seeking relief in respect of the balance of the amount claimed by way of refund. The Assistant Collector of Sales Tax by his order dated 4th September, 1958, granted further relief to the petitioners but that relief was also partial and was confined to a sum of Rs. 4,000-1-3. No refund order was, however, issued in favour of the petitioners pursuant to this order of the Assistant Collector of Sales Tax. Before we proceed further to state what happened in regard to this amount of Rs. 4,000-1-3 which was ordered to be refunded as aforesaid, we may point out that the petitioners being dissatisfied with the disallowance of the balance of the claim for refund by the Assistant Collector of Sales Tax, preferred a revision application to the Additional Collector of Sales Tax on 29th December, 1958, and that revision application is still pending. We are, however, not concerned with the balance of the claim for refund which is pending adjudication in that revision application. In the meantime on 14th October, 1958, the petitioners received a notice from the Sales Tax Officer calling upon them to show cause why the sum of Rs. 10,361-5-6 refunded to the petitioners should not be forfeited under section 21(4) of the Bombay Sales Tax Act, 1953, as the petitioners had not produced receipts from their purchasers showing that the amount returned had been refunded to them by the petitioners. This was followed by a notice dated 19th November, 1958, by which the Sales Tax Officer pointed out to the petitioners that the refund of Rs. 4,000-1-3 was being withheld as the same was to be adjusted against the amount of Rs. 10,361-5-6 which was proposed to be forfeited. The petitioners by their letters dated 28th November, 1958, and 16th December, 1958, challenged the right of the Sales Tax Officer to forfeit the amount of Rs. 10,361-5-6 refunded to the petitioners. The Sales Tax Officer, however, did not accept the contentions of the petitioners and by an order dated 24th March, 1958, forfeited