The Irken-Planet Jacker Treaty is a document signed at an unknown point in Irken History by the Irkens and the Planet Jackers, revealing that while the Irkens are an imperialistic race they still conduct occasional diplomacy with other species from time to time.
Mentioned only in Planet Jackers, one of its terms was that the Planet Jackers could not throw a planet marked for conquest by the Irken Military into their sun. Zim reminds the Planet Jackers of this. However, since Earth isn't marked as Zim isn't really an Irken Invader, Earth is open for the Planet Jackers to throw into their sun.
According to Almighty Tallest Red's voice actor Wally Wingert, it was organized by the Almighty Tallest, but he did not indicate which one initiated it, although is more than likely that Tallest Red did so as he is the smartest of the two.