A spokesperson from the International Telecommunications Union says Tonga does not own its orbital slots indefinitely.
Orbital slots are the areas allocated in space under an international treaty by the ITU, into which network satellites are launched.
A decision made by cabinet in May gave approval for the outright sale of Tonga's satellite orbital slots.
The public service association says parliament should have been consulted.
The PSA's seceretary general Mele 'Amanaki says the slots are national assets and should be protected and not sold.
The ITU allocates the slots and says they can only be assigned to registered members who apply for them and that no country has the rights to claim the slots indefinitely.
The ITU's constitution does not prevent the transfer of satellite networks between registered members.
But a spokesperson says there must be strong reasons otherwise a transfer could be construed as trafficking in the international orbit.