The companies, including Dow Chemical Co. (nyse: DOW - news - people) and Monsanto Co. (nyse: DOW - news - people), appealed a ruling by a U.S. appeals court in New York that the two plaintiffs had been inadequately represented in the 1984 settlement and cannot be bound by it.

The case involved Daniel Stephenson and Joe Isaacson, who both served in the U.S. military during the Vietnam War. They allege their exposure to Agent Orange, a herbicide sprayed by the U.S. military during the war, caused their illnesses.

Stephenson was diagnosed with multiple myeloma, a bone marrow cancer, in 1998, while Isaacson was diagnosed with non-Hodgkins lymphoma in 1996.

The companies in the 1984 settlement agreed to pay $180 million to veterans who were exposed to Agent Orange and then died or became ill. The payments were made for 10 years, and the settlement provided no payments for death or disability occurring after December 31, 1994.

U.S. District Judge Jack Weinsten, who presided over the settlement, dismissed the lawsuits by the two plaintiffs. He ruled the plaintiffs both were bound by the 1984 settlement.

But the appeals court disagreed, saying Stephenson and Isaacson had both learned of their alleged injuries only after the settlement fund had expired in 1994. It ruled they could not be constitutionally bound by the 1984 settlement.

The companies in appealing to the Supreme Court argued the decision opens up a new chapter in the long-resolved Agent Orange litigation and "undermines the legal peace" they paid $180 million to secure.

"Simply put, the ... decision ensures that defendants cannot settle with confidence that they have achieved peace from further litigation," the companies said in the appeal.

The Supreme Court will hear arguments in the case early next year, with a decision due by the end of June.