Defendant companies that are unable to persuade a judge to dismiss a case tend to settle with those that are suing - the better to protect business secrets from possibly being revealed by witnesses or documents in a trial.

Even more unusual is a defendant's claim of what antitrust lawyers call foreign compulsion. Using this defense, a company targeted in an antitrust suit argues not that it didn't do what is alleged, but that the government of its country forced that conduct. The seldom-tested principle holds that if it accepts this defense, a US court should dismiss the case at hand.

Providing evidence of compulsion is difficult, legal experts say, because a company could face recrimination at home if it disclosed to a court sensitive or possibly embarrassing information about a government directive to break US law.

That defense, however, is at the heart a trial that continues this week in US District Court in Brooklyn of Hebei Welcome Pharmaceutical Co Ltd and Weisheng Pharmaceutical Co Ltd. The two companies are accused of acting as a cartel and conspiring, unlawfully, both to fix prices and limit exports of raw vitamin C between December 2001 and June 2006.

Hebei Welcome and Weisheng are, respectively, units of North China Pharmaceutical Co and Hong Kong-listed China Pharmaceutical Group Ltd, both of which are also named as defendants.

The plaintiffs are a court-certified "class" that now numbers about 150 and consists mainly of food and beverage processors, nutritional supplement distributors and other direct buyers of vitamin C at a time when Chinese firms dominated a $500 million market.

A written agreement by the Chinese companies to set prices and limit exports, the US plaintiffs claim, caused spot-traded prices of vitamin C to soar to as much as $15 a kilogram by April 2003 from about $2.50 a kilo in 2001. The plaintiffs are seeking $54 million in damages, though US antitrust law allows a judge to triple that amount.

The suit was filed in 2005 by New Jersey-based food processor Ranis Co and Animal Science Products Inc, a Texas producer of supplements for livestock. But the trial was delayed by the Chinese companies' unsuccessful efforts to get the case dismissed.

In September 2011, US District Judge Brian Cogan rejected the "compulsion" rationale as grounds for shielding the defendants from enforcement of US law, a decision that allowed the case to proceed to trial. "The Chinese law relied upon by defendants did not compel their illegal conduct," he wrote.

In May 2012, a third defendant, Aland (Jiangsu) Nutraceutical Co Ltd, formerly known as Jiangsu Jiangshuan, agreed to settle the case for $10.5 million - $9.5 million to direct buyers of vitamin C and $1 million to indirect purchasers. On Wednesday, two Aland executives testified that their company faced penalties, including being barred from selling to foreign customers, if they didn't comply with the price and supply controls, which they said were set by the Ministry of Commerce through a commerce chamber.

The ministry filed a court brief in support of the defendants, saying a ruling against them would "improperly penalize" the vitamin companies for "the sovereign acts of their government and would adversely affect implementation of China's trade policy".

Cogan refused to allow that written assertion as evidence to be presented at trial, but in an earlier decision he said a retired Ministry of Commerce official, Qiao Haili, could testify, over the plaintiffs' objections.

In his opening statement, Daniel Mason, the attorney representing Weisheng, told jurors that the trial was "historic" and "unprecedented" and would include, for the first time in a US court, testimony from a former Chinese government official.

Mason said the Chinese and US governments view competition differently. Beijing, he said, had decided that vitamin C was a critical industry and sought to ensure coordination among companies on pricing and production.

William Isaacson, a lawyer for the plaintiffs, told jurors: "These companies met, agreed and conspired to increase prices in the US, contrary to our free-enterprise system."

James Southwick, who is also representing plaintiffs in the case, told China Daily before the trial that he doubted the litigation will have repercussions for US-China trade.

"This is a pretty straightforward case," Southwick said. "While it's [vitamin C] an important product, US-China relations exist on so many levels, this is not going to derail anything.

"If we win, it won't be a happy thing for the Chinese companies, but it won't be a shock to the trade relationship - it's robust."

Contact the writer at josephboris@chinadailyusa.com