Sydney Roosters centre Robert Toia stayed with Tonga despite attracting Kangaroos interest before this World Cup.
Australia's players are set to receive AUD$40,000 under a deal negotiated by the RLPA and ARLC in their collective bargaining agreement.
Players from other nations earn $850 per match, with a maximum of $4,250 if their team reaches the final.
Dolphins forward Felise Kaufusi, who represents Tonga but is not in its World Cup squad, became RLPA general president in November last year.
He told AAP: "I want more equality in the prize money. It is something we will raise in the next CBA."
National coaches warned the pay gap could encourage players to choose Australia for their families' financial benefit.
Kaufusi said most players prioritise heritage and culture, while fairer payments could remove money from the decision.
In 2017, Tonga captain Jason Taumalolo and former Cronulla prop Andrew Fifita chose Tonga, giving up the $20,000 offered to Tier One players.