Non Appealable decisions and orders :
As per section 121 of CGST Act, no appeal shall lie against any decision taken or order passed by a GST officer if such decision taken or order passed relates to any one or more of the following matters —
(a) An order of the Commissioner or other authority for transfer of proceeding from one officer to another officer; or
(b) An order pertaining to the seizure or retention of books of account, register and other documents; or
(c) An order sanctioning prosecution under the Act; or
(d) An order passed under section 80 [order granting or not granting instalments for payment of taxes].
These are overriding provisions.
Of course writ jurisdiction of High Court and Supreme Court is not affected.