WTO judges rejected a Chinese complaint in December against President Barack Obama's decision to impose three-year duties on $1.8 billion (11.7 billion yuan) of car and light-truck tires from China under a so-called safeguard provision designed to protect U.S. producers from a surge in imports.

The ruling added to tensions between the world's two largest economies, already strained by a Chinese trade surplus that was three times larger than forecast in April as exports surged to a record.

The two countries, which had 3 trillion yuan in annual two-way trade in 2010, have clashed over access to each other's markets for products including steel pipes, auto parts, poultry, movies and music.

China's trade surplus widened to a more-than-estimated 74 billion yuan last month, compared with 10.9 billion yuan a year earlier.

The Obama administration and U.S. lawmakers say China's currency policy gives the nation's exporters an unfair competitive advantage, costing American jobs.

The complaints filed to Obama by the United Steelworkers union, which represents 15,000 employees at 13 tire plants in the United States, were the largest safeguard petition to protect U.S. producers from growing imports from China.

The union said Chinese tire exports to the United States tripled from 2001 to 2004 to 41 million tires and called for an annual import cap of 21 million.