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Folau's four-year contract with Rugby Australia (RA) and the New South Wales Waratahs was torn up in May after he was found guilty of a "high-level" breach of RA's code of conduct for posting on social media that hell awaits drunks, homosexuals, adulterers and other groups.
The decision cost Folau a place in the Wallabies squad for the Rugby World Cup in Japan.
He had flirted with the idea of switching back to rugby league earlier this year but Australia's National Rugby League ruled out any move to the 13-man code.
The Tongan organisation, however, said they would welcome Folau and his younger brother John for their tests in New Zealand against Britain on October 26 and the Kangaroos on November 2.
"The Chairman of the Tongan National Rugby League, Mr George Koloamatangi, today announced that both Israel and John Folau will play for Mate Ma'a Tonga in the Oceania Cup to be played in late October, early November," the TNRL said on Facebook.
Folau confirmed the move in a statement issued by the TNRL, which said his selection had been approved by the sport's international governing body the Rugby League International Federation (RLIF).
"I don't want to bring any of my personal matters into this and I am grateful that the RLIF have endorsed my availability," Folau said.
"What I will do now is focus on playing great rugby league and do my talking on the field."
The RLIF said later on Monday that the TNRL statement was incorrect.
"The Rugby League International Federation is aware of a media release issued by Tonga National Rugby League stating that Israel Folau has been 'approved' by the RLIF to represent Tonga in international matches," it said in a statement.
"That statement is incorrect, the RLIF has not been formally asked to consider this matter. The RLIF will not be commenting further on this situation at this stage."
Folau, who used to play for National Rugby League teams the Melbourne Storm and Brisbane Broncos, has taken RA to the Federal Court saying he was unfairly dismissed on religious grounds.
He is seeking $5 million plus compensation for foregone sponsorship and future contract income from RA and his former Super Rugby side, the Waratahs.