Papua New Guinea opposition MP, Sir Mekere Morauta, says key agencies were sidelined in negotiations for the Papua LNG deal.
The government of Peter O'Neill has trumpetted the benefits that will accrue from the gas deal, led by French company Total.
But Sir Mekere, who is a former prime minister, said Mr O'Neill hijacked the approval process, putting state and landowner interests at risk.
He said Mr O'Neill shut out the State Negotiating Team and the Department of Petroleum, meaning the gas agreement was largely the work of private companies.
Sir Mekere said this risks royalties and development levies not being paid, as he claims happened with the earlier PNG LNG project.