BEIJING — Beijing trade officials on Sept. 14 filed a complaint with the World Trade Organization over new U.S. tariffs on tires imported from China, stepping up pressure on Washington in the latest in a series of trade disputes, according to The Associated Press. The conflict continues to escalate as Washington and Beijing prepare for a summit of the Group of 20 leading economies in Pittsburgh on Sept. 24-25 to discuss efforts to end the worst global downturn since the 1930s.

The escalation in tensions has some food industry insiders concerned. Earlier this month, an ad hoc coalition, which includes the National Pork Producers Council and 33 other food and agricultural organizations, voiced concern about actions U.S. Trade Representative Ron Kirk might recommend be taken against China over tires imported into the U.S. The group fears China may, in turn, retaliate against U.S. agricultural products. Pork and soybeans, for example, have been mentioned as candidates for retaliation, according to the N.P.P.C. (See: "

Coalition fears Chinese retaliation against U.S. food industry").

China’s complaint to the W.T.O. in Geneva triggers a 60-day W.T.O. process in which both sides are to try to resolve the dispute through negotiations. If negotiations fail, China can request a W.T.O. panel to investigate and rule on the case.

Beijing's rapid response to Friday's tariff decision shows the urgency China attaches to maintaining exports amid slumping global demand. President Barack Obama approved the higher duties to slow the rapid growth of U.S. imports of Chinese-made tires blamed for the loss of thousands of American jobs. Beijing criticized the move as a violation of free trade and called on other governments to oppose protectionism.

The Office of the U.S. Trade Representative in Washington said the U.S. had not stepped out of line.

As the world's largest and third-largest economies, the U.S. and China, respectively, have been embroiled in disputes in recent years over access to each others' markets for a variety of goods, including poultry, steel pipe, auto parts, movies and music.

President Obama acted under a provision in the U.S.-Chinese agreement on Beijing's accession to the W.T.O. that allows Washington to slow the rise of Chinese imports to give time to American industry to adjust, the White House said. Obama's order raised tariffs for three years on Chinese tires — by 35% in the first year, 30% in the second and 25% in the third.

The United Steelworkers, which brought the case in April, claims more than 5,000 tire workers have lost jobs since 2004 as Chinese tires flooded the U.S. market.

Beijing announced Sept. 13 it would investigate complaints that American chicken and auto products are being dumped in China or benefit from subsidies. U.S. imports have "dealt a blow to domestic industries," the ministry said.