( 1 ) IN this group of petitioners, a common question of vires of Sec. 15-B of the Gujarat Sales Tax Act, 1969 as amended by Sec. 2 of the Gujarat Sales Tax (Amendment) Act, 1990 arises for consideration. It is the contention of the petitioners that the said provision is beyond the legislative competence of the State legislature. In order to appreciate this common grievance of the petitioners, it is necessary to note a few introductory facts :

( 2 ) I. Introductory facts : The petitioners are dealers registered under the provisions of the Gujarat Sales Tax Act, 1969 (the Act for short ). They carry on the activity of manufacturing and selling various goods in this State. For that purpose, they require raw materials which are to be used in manufacturing the end product. The materials purchased by them in the State and used in the manufacturing process have been subjected to purchase tax by the impugned provision. The petitioners contend that the State Legislature has no competence to impose such tax as such tax does not fall within any of the entries of List ii of the Seventh Schedule to the Constitution, viz. ,the State list especially Entry 54 thereof. They have joined