A group of prominent legal professionals, academics and political leaders has written to the negotiators of the Trans-Pacific Partnership calling on them to reject a provision that would allow investors to sue governments directly.
The TPP agreement would cover Pacific Rim countries, including the United States and New Zealand.
The open letter expresses concern that foreign investors are being granted greater rights than are provided to domestic firms and investors under the constitutions, laws and court systems of host countries.
Signatory Professor Bryan Gould says this would mean a significant loss of the power of democratic self-government.
He says governments could even be ordered to stop their courts from enforcing their own decisions.
The letter will be delivered to the lead negotiators of each country at the start of the round of TPP negotiations in Dallas, Texas on Wednesday.
The nine countries involved in the TPP are Australia, Brunei, Chile, Malaysia, New Zealand, Peru, Singapore, the United States and Vietnam.