WASHINGTON—The U.S. government moved to impose substantial punitive tariffs on hundreds of millions of dollars of imported steel products from South Korea and eight other countries, a much-anticipated decision that marks one of the largest anti-dumping cases in recent memory.

BENTON HARBOR, MI—The Commerce Department has ruled that Whirlpool Corp. and other U.S. appliance assemblers are being harmed by competitors importing certain refrigerators from South Korea and Mexico. The department found that Samsung, LG, Electrolux and other brands were illegally “dumping” some of their foreign-made appliances in the United States by selling the products at less than fair value.