A provision that would let foreign corporations challenge new American laws and regulations has become the latest flashpoint in the battle over the Trans Pacific Partnership trade agreement, even as President Obama on Tuesday said he will renew his push for its passage in the lame-duck session of Congress.

“We’re in a political season now and it’s always difficult to get things done,” Obama said at a town hall meeting in Laos. “So after the election, I think people can refocus attention on why this is so important.” He sounded confident: “I believe that we’ll get it done.”

The latest salvo from opponents of the deal came in the form of a letter to Congress signed by hundreds of law professors and economists – including Laurence Tribe, who taught Obama at Harvard – protesting the inclusion of “Investor State Dispute Settlement” (ISDS) provisions in the TPP agreement.

The ISDS provisions would empower corporations who object to U.S. laws and regulations that cut into their profits to sue the United States before an international arbitration panel. The signatories to the letter write that this “system undermines the important roles of our domestic and democratic institutions, threatens domestic sovereignty, and weakens the rule of law.”

Senator Elizabeth Warren, D-Mass., a leading critic of the ISDS provisions, introduced the letter on a conference call hosted Wednesday by the advocacy group Public Citizen.

“It’s about leverage,” Warren said. “Leverage for big companies to threaten an intimidate governments who might dare take action that threatens their profits.”

She cited the example of Canada being successfully sued under ISDS rules contained in the North American Free Trade Agreement (NAFTA) by a U.S.-based company that was denied a permit for an open-pit mining project.

Listen to the call: