WASHINGTON (Yonhap) -- Four senior U.S. senators are pressing trade authorities to step up measures to defend Whirlpool Corp. from tough competition with its Korean rivals.

Whirlpool, a Michigan-based appliances maker, has filed a series of petitions with the Commerce Department, claiming Samsung, LG and Daewoo have dumped goods produced in Korea and Mexico, and even taken advantage of government subsidies.

Senators Carl Levin (D-MI), Debbie Stabenow (D-MI), Rob Portman (R-OH) and Sherrod Brown (D-OH) sent a letter to Commerce Secretary John Bryson last week calling for the "strong enforcement of trade laws in the ongoing anti-dumping and countervailing duty investigations" requested by Whirlpool, according to congressional and diplomatic sources on Sunday. Ohio is home to Whirlpool's five factories.

They pointed out that Whirlpool has more than 22,000 employees in the U.S. and said job-creating firms like Whirlpool should not be "handicapped by unfair trade practices perpetrated by their foreign competitors."

The senators took issue with some business practices of South Korea's major conglomerates, known as chaebol.

The U.S. should explore ways "in which the Korean chaebol system and the relationships between the large Korean conglomerates and their much smaller suppliers may mask the true measure of prices and costs," they said.

Sen. Brown separately said, "I am urging the Obama administration to be aggressive in investigating the unfair trade practices of Whirlpool's competitors, who make their products in South Korea and Mexico."

Sen. Portman, a potential vice presidential running mate for Republican Mitt Romney, also called on the government to continue to investigate the "harmful practices of foreign companies who cut corners and put domestic companies at a competitive disadvantage."

Whirlpool has been constantly losing market shares in the United States to South Korean companies, especially in selling refrigerators and washing machines.