The International Centre for Settlement of Investment Disputes has ordered Papua New Guinea's government to stop interfering in the management of PNG Sustainable Development Program.
The dispute arose in late 2013 when the Peter O'Neill-led government moved to assume complete control of the 63 percent share of the lucrative Ok Tedi mine that SDP had held until then.
As well as the case going to arbitration, the SDP, chaired by former prime minister, Sir Mekere Morauta, is suing the government in the courts in Singapore, where the SDP is registered.
The ICSID has rejected the PNG government's objections to arbitration of the expropriation of Ok Tedi Mine Ltd shares.
The government last month announced the people of Western Province were to be given one third ownership in Ok Tedi Mine Ltd.
Now, the ICSID has ordered the government to refrain from disposing of OTML shares to third parties.