WASHINGTON—Attorneys general from 16 U.S. states have opposed a Trump administration proposal to ship LNG by rail, arguing that potential leaks from the shipments pose risks of fiery explosions to residents and emergency responders.

The top legal officers of Maryland, New York, California and other states on Jan. 13 filed comments urged the Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) to withdraw the proposal pending the completion of safety studies and the development of an environmental impact statement.

The Trump administration proposal would help natural gas drillers desperate to export the fuel because of a glut.

“The administration is bending to the will of the fossil fuel industry ... and it puts at risk neighborhoods, towns and cities across our nation,” said Maryland Attorney General Brian Frosh.

It could also benefit rail operators, who have suffered as coal output has fallen to the lowest level since 1975.

The attorneys general warned that the proposal could allow LNG unit trains of up to 100 cars operated by just one person. They said LNG—natural gas that is super-cooled into a liquid for transport—sent by rail raises the risk of spills that can form highly flammable, ground-hugging vapor clouds.

PHMSA’s proposal said that a specially-built rail car known as DOT-113 is designed to handle super-cooled liquids. But the attorneys general said that PHMSA and another agency have not completed safety testing of transporting LNG in the cars.

A PHMSA spokesman said safety is the top priority and that the agency will evaluate all of the public comments and concerns raised in the rulemaking process.

In December, PHMSA approved the use of trains to ship LNG from northeastern Pennsylvania to southwestern New Jersey.

Energy Transport Solutions, a subsidiary of New Fortress Energy, hopes to liquefy Pennsylvania gas and send it by rail to a not-yet-built terminal on the Delaware River for shipping to global markets. The route could take LNG through populated cities Philadelphia and Camden. Previous rail approvals have been made for companies in Florida and Alaska.

PHMSA’s December approval included a special permit that imposed several operational controls for safety. But the attorneys general said it did not meet minimum controls urged by the National Transportation Safety Board, an independent federal agency, including restrictions on routing through populated areas.

The American Association of Railroads, an industry group that supports shipping LNG by rail, said railroads move more than 99.99% of hazardous materials to their destination without releases caused by an incident, and the industry has worked with government and others to strengthen tank car standards.