Unrevealed, but with contradictory vague clues.
Spoiler:
The Veskarium? Unlike the isolationist Azlanti Star Empire, the Veskarium is known to have worked with the Order in the past. If the Veskarium government did hire the Order, however, they did so without informing their representatives on-site.
The Azlanti Star Empire? The Order tries to leave the system as soon as the Azlanti reinforcements arrive, suggesting that the Star Empire may have quietly hired the Order simply to keep a lid on the situation until they could muster their forces.
The Pact Worlds? Seems quite unlikely, since this makes the Order de facto allies to the PCs out of the gate. Could be a powerful special interest within the Pact Worlds, though, such as a discreet AbadarCorp looking to keep trade flowing.
An Unknown Third Party? Maybe? he said, with shrug.
I think the real answer is: "Don't sweat it, this doesn't matter for the purposes of this adventure."