GST rules amendment clarifies job worker challan endorsements and strengthens Authority governance and investigatory referral powers. Amendments allow challans for goods moved between job workers to be issued by the principal or the sending job worker and to be successively endorsed indicating quantity and description; designate as Secretary to the Authority an officer not below the rank of Additional Commissioner in the Directorate General of Safeguards; prescribe a quorum of members and majority decision-making with the Chairman's casting vote; permit the Authority to refer matters back to the Director General of Safeguards for further investigation where a report indicates (non-)contravention but additional inquiry is warranted; and exclude leasing of parcel space by railways from expressions concerning transport of goods by rail.