Section 122(b) in The Central Goods and Services Tax Rules, 2017
(b)four Technical Members who are or have been Commissioners of State tax or central tax [for at least one year] [Inserted by Notification No. G.S.R. 1165(E), dated 15.9.2017 (w.e.f. 19.6.2017).] or have held an equivalent post under the existing law, to be nominated by the Council.