The Trump administration is at odds with American companies over a proposed rule change to the North American Free Trade Agreement that is endangering a bright spot—energy—in contentious treaty talks.

All three Nafta countries—the U.S, Canada and Mexico—agree that a new treaty should aid the burgeoning energy trade. Under negotiation are initiatives to ease the construction of pipelines across borders, to aid U.S. exports of natural gas and to assist American companies opening gas stations or explore for oil in Mexico, officials say.

The proposals would also prevent Mexico from backsliding on liberalizing of its energy sector at a moment when American industry is seizing a growing role in Mexican energy.

U.S. businesses, however, including some energy companies, are balking at Washington’s pursuit of an unrelated rule change that would weaken or end Nafta’s protection of U.S. investments in Mexico or Canada from government intervention.

At issue is the Investor-State Dispute Settlement, which allows a U.S. business to take legal action if a foreign government harms the company’s investment in that country. For example, if the Mexican government nationalized, say, a U.S-owned oilrig in Mexico, the measure would give the American company the right to appeal to adjudicating panels set up under Nafta.