Gst for gta

One of our clients is a GTA registered under GST. As per the GTA taxation norms, GST need not be collected from GST registered parties and 6 others for consignment & should be levied on reverse charge basis. Now, is this rule applicable for unregistered GTA or also for registered GTA?. Because, since the GTA is registered, the contract is clearly between two registered parties. i.e. the consignor and the GTA. Now, how come reverse charge comes in place here? Kindly clarify my doubt on this issue.