A group of lawmakers is urging Obama administration officials to oppose a multinational U.S. company's efforts to sue Peru in a mining dispute, citing the company's environmental and health record.

The request, made in a letter last month to Secretary of State Hillary Clinton and Treasury Secretary Timothy Geithner, pits the lawmakers against a secretive billionaire and big U.S. political donor—and, in some cases, against themselves.

Four of the letter-signers—Reps. Bobby Rush, D-Ill., Lynn Woolsey, D-Calif., Ed Towns, D-N.Y., and Danny K. Davis, D-Ill.—have switched sides in a controversy involving Doe Run ...