General Motors and some US lawmakers reportedly are criticising Japan for what they call discriminatory and arbitrary government policies that threaten free trade between the two countries.

Testifying at the House of Representatives, GM chief economist Mustafa Mohatarem said currency manipulation by Japan has given its automakers an unfair advantage in the US market, hurting American manufacturers, the Associated Press (AP), reported.

GM reportedly said Japan's weak yen policy gave Japanese automakers a cost advantage ranging from $US3,000 on a small car to $12,000 on a luxury sport utility vehicle.

"This subsidy has both facilitated the expansion of Japanese companies in the U.S. and succeeded in keeping American-built automobiles out of Japan," Mohatarem said, according to the report.

Representative Bill Thomas, chairman of the House Ways and Means Committee, said US-Japan trade is stagnating "in large part because the Japanese have built a wall of complex protectionist practices and regulatory systems."

He added that Japan's trade attitudes are "caused by its heavy-handed and bureaucratic industrial policy, which is often imbued with political patronage that pulls down every aspect of the economy."

According to the Associated Press, Wendy Cutler, the assistant US trade representative for Japan, said the US-Japan trade relationship is "rich in complexity" and has moved from largely acrimonious to cooperative in recent years.

Japan, she reportedly said, is the fourth largest US goods trading partner, with $180 billion in total two-way trade last year.

While Japan has made inroads in opening trade, "old ways die hard in Japan," Cutler said, according to AP.