The lawsuit, to be filed in the US district court for the District of Columbia, is a class action, which means the plaintiffs will receive nothing if they lose. But it is thought likely to open the door to future legal action.
In what is believed to be the first legal challenge of its kind to the biotechnology industry, Monsanto and other companies are to face action in a US court.
A lawsuit alleges that Monsanto has formed a global cartel with "other biotech companies named as co-conspirators". It is brought by a legal consortium headed by a New York law firm, Cohen, Milstein, Hausfeld and Toll.
The firm has not so far named the other companies it is accusing of belonging to the alleged cartel.
'Landmark allegations'
It is arguing that the alleged cartel has "forced genetically-modified (GM) seeds onto the market at fixed prices without sufficient testing for safety to human health and the environment".
The lawsuit alleges "violations of US anti-trust law, public nuisance, deceptive trade practices and breach of implied warranty".
It also includes what the firm describes as "landmark allegations" that Monsanto "violated customary international law".
'Products safe' - Monsanto
Monsanto said it would fight the lawsuit. "We're people who use these products, too. We're not going to introduce something into the market that is unsafe for families," said David Snively, an attorney for the company.
Monsanto said it spent tens of millions of dollars and years to field-test each new plant variety for safety.
And although fewer than a dozen companies dominate the development and sales of GM seeds, there is fierce competition among them, Mr Snively said.
Treble damages
The consortium bringing the lawsuit is working with environment and development groups, including the National Family Farm Coalition and the Foundation on Economic Trends.
The lawsuit, to be filed in the US district court for the District of Columbia, is a class action, which means the plaintiffs will receive nothing if they lose. But it is thought likely to open the door to future legal action.
The plaintiffs say they are seeking "treble damages for anti-trust violations, compensatory and punitive damages, and injunctions compelling Monsanto to sufficiently test GM seeds and crops for human health and environmental safety, and an end to the operation of Monsanto's cartel".
Cohen, Milstein, Hausfeld and Toll have links with several foreign law firms, including the British legal practice Mishcon de Reya. BBC News Online has been told it is likely that the US lawsuit will lead to a similar action in the British courts.
Failure to regulate
Andrew Simms, of the London-based New Economics Foundation, told BBC News Online: "The World Trade Organisation meeting in Seattle was chaos".
"That was because many people feel the world is being organised for a wealthy minority regardless of the consequences for anyone else. This lawsuit is evidence of that feeling.
"And regulation has not caught up with the reality of the global market place. Unless regulators do get to grips with it, people will be left to cope with anything that a handful of corporate cartels wishes to dump on them."