North American wheat farmers are seeking $1bn (£540m) in damages from Australian wheat exporter AWB, claiming it has used corruption to win business.
Exports to Iraq play a major role in Australia's wheat industry
They have filed a class action in Washington, using US anti-racketeering laws designed to fight organised crime.
AWB is accused of using bribery and corrupt means to win grain sales in Iraq, Yemen, Pakistan and Indonesia, at the expense of US and Canadian farmers.
AWB said it would "vigorously defend" any action brought against it.
The Australian government has already initiated an investigation into AWB, following up claims that the exporter spent $220m bribing officials from Saddam Hussein's Iraqi government to secure $2.3bn of wheat contracts under the United Nations oil-for-food programme.
It has admitted to, and apologised for, the bribes.
The North American farmers have said that they will pursue their legal action using evidence obtained by the Australian inquiry and another undertaken by the UN.
Australian press reports said that the farmers' claim accused AWB of conspiring to use tactics including bank fraud, bribery and money laundering.
As well as the Iraq allegations, the claim says the company bribed officials in Yemen and Pakistan and sabotaged the Indonesian market to keep out US grain exports.
Six farmers are named on the class action, which has been filed against a US subsidiary of AWB.