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