Environmental groups opposed to U.S. natural gas exports just found an unlikely ally: the Commodity Futures Trading Commission.

The government agency that regulates futures and options markets found that shipping gas overseas could raise costs for Americans. Domestic prices could rise as much as 20 percent due to the burgeoning industry that liquefies gas so it can be shipped around the world on tankers, according to a CFTC report.

In its study, the CFTC cited other assessments conducted by the American Petroleum Institute, the U.S. Energy Department and Deloitte LLP.

The U.S. shale boom has bloated domestic gas supplies and ushered in a new era of American energy exports. President Donald Trump has encouraged the development of more LNG plants, while groups such as the Industrial Energy Consumers of America have panned exports as a drain on the nation’s resources.

“Estimates of U.S. LNG export levels and price impacts on domestic markets vary widely, but generally these estimates suggest that there is a potential for U.S. domestic natural gas markets to be influenced by global supply-demand factors,” the commission said in the report.