The U.S. livestock industry has asked the U.S. government for assistance in lifting South Korea’s ban on imports of American beef from cattle older than 30 months of age. 

The National Cattlemen’s Beef Association made the request in a letter to the Office of the U.S. Trade Representative on Tuesday, calling the restriction an unfair trade practice. 

The association reportedly said it understands that the 30-month age limit on U.S. beef is a sensitive issue in South Korea, but called it an issue that cannot be ignored.

It claimed that China, Japan and Taiwan lifted similar bans in recognition of the safety and quality of American beef.

Under a 2008 agreement, South Korea imports U.S. beef only from cattle under 30 months of age due to concerns over mad cow disease.