The United States has "political reasons" for considering a bill that would keep in place the countervailing duties that are now charged on various goods imported from China, said former Chinese trade officials.

On Monday in the US, the Senate unanimously passed a law that would allow the US Commerce Department to continue to levy nearly $5 billion in tariffs on imports it believes to be subsidized from China and Vietnam, although a US court has deemed the practice illegal.

The House of Representatives is expected to vote on the bill as early as Tuesday in the United States. If passed, it will then go to President Barack Obama for a signature.

The former trade officials called on China to take a tough stance and fight against the policy if the bill is passed.

As the US presidential election draws near, "the US is trying all means to gain votes by making these issues with China into political issues", said Sun Zhenyu, former ambassador to the World Trade Organization and a representative of the National Committee of the Chinese People's Political Consultative Conference.

"If the legislation is passed, China should appeal to the WTO without any hesitation."

In December, the US Court of Appeals for the Federal Circuit said the US countervailing-duty law should not be applied to non-market economies, which is what many countries consider China to be.

The court also said the Department of Commerce should not be imposing countervailing duties on goods from China, saying that government payments made in a non-market economy should not be regarded as subsidies.

The ruling came after the Chinese tire maker Hebei Starbright Tire Co Ltd filed an appeal with the US Court of International Trade in response to the Department of Commerce's announcement in August 2008 that a 14-percent countervailing duty would be levied on products imported by Hebei Starbright Tire.

"The US move is pure trade protectionism," said Zhang Zhigang, director of the Council of China Foreign Trade and also a former vice-minister of commerce. "China should strongly oppose it and retaliate if such a law were eventually passed.

"It's unfair that the US did not recognize China's market economy status when China entered the WTO in 2001. And it is absolutely unreasonable if the largest economy in the world plans to charge countervailing duties on Chinese exports when the US doesn't recognize China's market-economy status."

Experts said the trade frictions between China and the US are expected to increase throughout the year, especially as the election campaign heats up.

Last week, Obama signed an executive order establishing the Interagency Trade Enforcement Center to investigate whether China and other US trade partners "play by the rules".

Since November 2006, the US has undertaken 30 countervailing duty probes against Chinese products, according to US figures.

The Club for Growth, an anti-tax advocacy group based in Washington, expressed opposition to the bill, saying "these duties restrict economic liberty and are anti-growth.

"We strongly urge members of Congress to defeat this proposal."