FAIRMONT, W.Va.—Clifton Tennant started mining coal in 1964 and spent nearly three decades working at Eastern Associated Coal Corp.'s Federal No. 1 mine, where he was knocked unconscious once by a piece of coal and another time by a 450-volt wire.

Since retiring from the mine in 1991, he has had prostate cancer, lost vision in his right eye and had a stroke. Now at the age of 76, he may lose his health insurance because a successor company he never worked for, Patriot Coal Corp., is asking a bankruptcy-court judge to throw out the union contract that guarantees retirement benefits for him and his wife, Loretta.

His wife, a retired teacher's aide, has kidney disease, Mr. Tennant says. If they lose benefits, they will have to buy insurance on their own or rely on Medicare and pay more for prescriptions and medical treatment, which he says they couldn't afford.

"If our benefits were cut off, we wouldn't last long," says Mr. Tennant, who lives in a neat modular home about a mile from his old mine. Now shut, it was once the world's most productive coal mine, with tunnels stretching 14 miles across.

On Thursday, Patriot Coal of St. Louis asked a judge in U.S. Bankruptcy Court for the Eastern District of Missouri to terminate benefits for about 10,000 retired miners and 13,000 dependents.