SYDNEY (AFP) - Hundreds of Australians who became sick after drinking soy milk containing dangerously high levels of iodine have widened their class action to include two Japanese companies, lawyers said.

About 600 Australians became ill after consuming Bonsoy milk, many suffering thyroid problems, up until the product was withdrawn from sale in late 2009, Maurice Blackburn Lawyers said on Thursday.

The case against the Australian brand owner Spiral Foods launched in the Victorian Supreme Court in 2010 had been widened to include manufacturer Marusan-ai Co Ltd and exporter Muso Co Ltd, the firm said.

"We say that these three companies had test results in mid-2006 which showed that Bonsoy contained extremely high levels of iodine, but they did nothing," said senior associate Irina Lubomirska in a statement.

She said the companies had breached consumer protection laws in Australia and Japan.

"None of the three companies did anything to ensure that Bonsoy, which was marketed and sold as a premium health food soy brand, was in fact safe to consume," she said.

The class action alleges that Spiral requested a reformulation of Bonsoy to include iodine-rich kombu instead of adding salt and as a result, the product had contained excessive iodine since mid-2003.

It also alleges that consumer concerns about iodine were repeatedly dismissed.

Victims are seeking compensation for medical expenses and loss of income as well as for the pain and suffering.

By the time Bonsoy was recalled in late 2009, after Australian authorities discovered that one glass contained seven times the upper safe dose of iodine for adults, it had been on the market for six years.

Because it was touted as a healthy product, some consumers had increased their intake when they became ill, Ms Lubomirska said.

A directions hearing on the matter is scheduled for March 8.