"But what I am really trying to understand is . . . Australia's resistance to any language on tobacco, and its seeming lack of interest in working on language that would protect Australia and others from future tobacco trade-based litigation."

Australia has required tobacco products to be sold in plain packages since December 2012. Attempts by companies including Philip Morris to overturn the law were defeated in the High Court. But it is now trying to sue Australia in the United Nations Commission on International Trade Law using an investor-state dispute settlement clause in an obscure Australia-Hong Kong agreement.

Most of the 12 nations taking part in the Trans-Pacific Partnership talks want to protect their rights to enact similar legislation in the face of a US insistence that the agreement include clauses allowing private corporations to sue governments.

"I never thought Australia would be a major problem in this effort, but we repeatedly hear that it is," the email says.

Australia's Trade Minister, Andrew Robb, has indicated he is prepared to trade Australia's previous opposition to investor state dispute settlement clauses in exchange for greater access to markets for commodities such as sugar.