He was the flamboyant lawyer who championed thousands of impoverished banana plantation workers in a battle against US corporations which allegedly poisoned them with pesticides.

Juan Dominguez left his penthouse office and Ferrari in Los Angeles to collect witness testimonies in dusty Nicaraguan villages and build a class action suit which could net his clients billions of dollars in compensation. It was his mission, he said, to stand up for the "little guy".

Hollywood could have made the cigar-chomping attorney into a Latino Erin Brockovich who delivered justice to field labourers left sterilised by dangerous chemicals. Except for one problem: Dominguez has been accused of orchestrating an audacious international fraud and cover-up.

A US judge has ordered the California state bar association to investigate the lawyer for recruiting fake witnesses and falsifying medical evidence. The scandal threatens to unravel hundreds of related cases involving more than 10,000 banana workers in central America.

Dole Food Company, the world's largest producer of fresh fruit and fresh vegetables and the main target of the suit, is celebrating what it hopes is a knockout blow. "It's a very important ruling," said Ted Boutrous, one of Dole's lead lawyers. "We think the fraud that has been exposed should bring these other cases to a rapid ending. It's already having a domino effect."

The cases revolve around the spraying of DBCP, or dibromochloropropane, a worm-killing pesticide, on banana plantations in five central American countries in the 1970s. Labourers say it damaged their health and, in the case of men, left them sterile. Dole denied causing any harm.

Local courts awarded damages - Nicaragua alone awarded more than $2bn (£1.2bn) - but were unable to force the corporations to pay. That changed when US courts became involved. In 2007 a Los Angeles jury awarded $5.7m to six Nicaraguan men who sued Dole and chemical companies.

Related cases were launched in California and Florida courts by thousands of plaintiffs from Panama, Guatemala, Honduras, Costa Rica and Ivory Coast. Potential awards were enormous.

In a dramatic twist Dominguez, a lead lawyer for the workers, became the accused. Investigators from Dole presented evidence that in two lawsuits Dominguez's legal team falsified work histories and laboratory reports. People who never worked on plantations were allegedly coached to lie and had children airbrushed out to shore up claims of sterility.

Los Angeles county superior court judge Victoria Chaney threw out the lawsuits in June. "The actions of the attorneys in Nicaragua and some of the attorneys in the United States, specifically the law offices of Juan Dominguez, have perverted the court's ability to deliver justice." Dominguez is expected to face contempt charges later this month.

Dole, which has 75,000 employees and $7bn revenues, has claimed vindication. "When a light is shined upon these cases they fall apart," said Boutros. The company now hopes to squash other cases which Judge Chaney said had been permeated by fraud.

Attorneys who represent banana workers in other cases complained that the ruling was too sweeping and undermined legitimate evidence that Dole ignored safety guidelines and harmed impoverished labourers with DBCP.

Dominguez, who did not respond to interview requests for this article, has challenged the judge's impartiality and noted that Dole's investigation did not identify the Nicaraguan witnesses who blew the whistle on him.

The Cuban-American's image still smiles from LA buses advertising his personal injury law firm. According to its website it has won over $65m in different cases.

Dominguez features prominently in a documentary, Bananas!, which depicts the plantation workers' efforts to bring their claims to court. The 87-minute film, made before the fraud findings, shows Dominguez in his swanky LA law office and in sweaty villages in Nicaragua. He visited more than 70 times over seven years, all on his own dime.

Dole is now suing the Swedish filmmaker, Fredrik Gertten, for allegedly making propaganda for a crook. Gertten, 53, said the film was a balanced portrayal and that the US food giant had a case to answer.

"Dole has been very successful in selling itself as the victim. In the film Dominguez is portrayed as a very colourful personality, which he is. I make it clear he is not a classical human rights-type lawyer."

The film has been shown in festivals in the US and Gertten hopes it will soon have a theatrical release in the US and Europe, including Britain.

He acknowledged Dominguez possibly lost control of some colleagues, and that fraud may have occurred, but said powerful corporations had reason to destroy him. "I think they used Juan Dominguez to show all the other plaintiffs' lawyers: don't do this."