The move could signal the start of more trade tensions between the massive trade partners at a time when the two economic powers were expected to lead the way out of the global financial crisis. 'This case is perceived as a turning point in U.S.-China relations and likely to represent a trend toward subtle, if not overt, forms of protectionism from both sides,' said James Zimmerman, a partner in the law firm Squire Sanders & Dempsey in Beijing. 'American business in China should be prepared for what might be a zealous retaliatory response from China, which might impact a broad range of U.S. commercial interests.' At the urging of U.S. International Trade Commission, a federal agency, President Barack Obama announced Friday that he would impose a 35 percent duty on automobile and light-truck tires imported from China. The decision was a major victory for U.S. labor unions but was opposed by myriad American business groups, including leading tire manufacturers and agricultural groups who rely on the Chinese market. Chinese officials lambasted the decision, accusing the U.S. of engaging in protectionism and violating World Trade Organization rules. They argued that the U.S. tire industry had long abandoned the low-end market that China covets and said Chinese tire imports had only increased by 2.2 percent between 2007 and 2008, state media reported. By announcing the investigation of American imports, the Chinese Ministry of Commerce signaled that it was prepared to challenge Obama's decision. 'Recently, the commerce ministry has received word from domestic industries indicating that (chicken and auto) products had entered our nation's markets via dumping, subsidies and other unfair trade means,' the ministry said on its Web site, giving no details about the specific products. The U.S. exported $1 billion worth of auto products to China in the first six months of this year, up 9.1 percent from the same time last year, state media said. American agriculture groups had written to Obama opposing the tariff, saying the Chinese market was the difference between being profitable and unprofitable for many. When China joined the WTO in 2001, it agreed to safeguards that allowed the U.S. to impose duties if it was determined that a surge in Chinese imports threatened American producers and caused a market disruption. The United Steelworkers estimated that 4,000 to 5,000 U.S. tire manufacturing jobs have been lost since 2004 as a result of Chinese imports. State media said an estimated 100,000 Chinese jobs and $1 billion in exports could be lost due to the tariffs, which would begin Sept. 26. 'It was a misuse of the special safeguard measures and sent a wrong signal to the world,' Chen Deming, China's minister of commerce, said Saturday. 