Trade Protest Is Planned on Eve of a Chinese Leader's Visit Battery assembly workers for the Wanxiang Group, an auto parts maker, in Hangzhou, China. HONG KONG - As the White House prepares for a Washington visit by the man who is expected to run China for the coming decade, trade tensions between the United States and Beijing are on the rise. Adrian Bradshaw/European Pressphoto Agency Making parts for transmission systems at Jiangling Getrag in Nanchang, China. On Tuesday, a coalition of big American labor unions, Democratic politicians and trade advocacy groups plans to start campaigning for the Obama administration to file a series of trade cases against China in the auto industry. They accuse Beijing of unfairly subsidizing Chinese auto parts makers and illegally restricting the exports of crucial raw materials that foreign parts makers need to stay competitive. The group says a 900 percent increase in auto parts imports from China over the last decade, to nearly $12 billion a year, is to blame for job losses in Michigan, Ohio and Pennsylvania - three swing states that the administration cannot easily ignore in a presidential election year. "The Chinese have cheated," said Senator Sherrod Brown, Democrat of Ohio, who is a Congressional leader of the trade effort along with Senator Debbie Stabenow, Democrat of Michigan. The group has been preparing its campaign for months. But it may be sensing a new opportunity after President Obama signaled a tougher trade stance against China in his State of the Union address last week, saying he would set up a trade enforcement unit to investigate unfair Chinese practices. Separately, the Commerce Department is considering whether to levy punitive tariffs against China over green energy technology. And on Monday, Washington was on the winning side of a World Trade Organization ruling against China for its export restrictions on industrial minerals. All of which promises to test diplomacy on both sides during a Feb. 14 White House visit by China's vice president, Xi Jinping, who is expected to succeed President Hu Jintao next winter as China's leader. Chinese officials have vehemently denied that they violate international trade agreements. "Over the past 10 years, China has fully implemented its W.T.O. commitments, and its trade and investment liberalization and facilitation have been significantly increased," President Hu said last month. Senator Brown said Washington's appetite for a more assertive trade policy was whetted last month by China's imposition of steep tariffs on $4.9 billion a year of imports of sport utility vehicles and large cars from the United States. Hoping to reduce the trade tensions just before Mr. Xi's visit, Chinese officials are preparing to send at least six business delegations on buying trips to the United States, people familiar with the plans but not authorized to discuss them said. Similar delegations have preceded past visits by top Chinese leaders to Washington and have focused on bundling planned purchases of Boeing jets, American grain and other exports into multibillion-dollar contracts that can be signed at elaborate ceremonies. The Obama administration has also made a few small conciliatory moves. The Commerce Department planned to issue a preliminary ruling on Feb. 13 on whether to impose tariffs on Chinese solar panels to offset reported Chinese export subsidies. But when the United States and China agreed last week that Feb. 14 would be the date for Vice President Xi's visit to Washington, the department pushed back its ruling until March 2. But small gestures may not overcome the shock among American trade officials and auto industry executives last month when China imposed the tariffs on American vehicles. An adviser to the Chinese commerce ministry, who insisted on anonymity because he was not authorized to comment, said that decision had been based mostly on jockeying among Chinese factions over the need to show toughness toward the United States and did not signal a broader shift in Chinese policies. The Chinese move came as American labor unions, Democratic politicians, policy research groups and trade lawyers were already in the final stages of the auto parts campaign that they plan to announce in Washington on Tuesday. Besides numerous Democratic members of Congress, the coalition includes the United Steel Workers union, the United Automobile Workers union, the labor-backed Economic Policy Institute and the trade law firm Stewart and Stewart, as well as the Wessel Group, a trade strategy firm.