The Interspecies Trade Alliance is an entity between various species, allowing the sharing of goods by means of trade. All ships had to remain on certain routes as not all species allowed free reign for the cargo ships.
The Federation, the Romulans, the Klingons and the Gorn were all part of the Alliance. The Tholians were skeptic about the treaty, and occasionally attacked Gorn ships, one of which belonged to Captain Kkossa. (PIO: "On a Knife Edge")