By Jon Leyne BBC Washington correspondent

A group of workers who claim they developed cancer through their jobs in the electronics industry are to begin what could be a landmark legal action in the US state of California.

Three former IBM workers and the family of a fourth, who has since died, say they were exposed to dangerous chemicals through their work in so-called "clean rooms", where microchips and other electronic parts are made in a dust-free environment.

It is the first of what could be hundreds of actions by former employees of IBM and other electronics companies in the US and in Britain.

The test case follows years of argument over the safety of working in such clean rooms.

Financial implications

Lawyers for the group argue the clean rooms are designed to protect the products but not the workers.

They say the former employees developed cancer after being exposed to a range of poisonous chemicals day after day.

The lawyers say the companies' own records show that over a period of years, workers in IBM clean rooms developed more of certain types of cancer and died younger than the rest of the population.

IBM says that is simply not true.

Hundreds more cases in the United States and Britain could depend on the outcome of this trial, which is being heard at a courthouse in California's Silicon Valley.

The financial implications for the industry are enormous.