Dow Chemical was ordered pay more than $400m (€300m) in damages after a federal jury on Wednesday determined that the US producer had fixed prices for isocyanates.
The plaintiffs, buyers of the products, had asked for $1.125bn in damages.
"While Dow is disappointed that the jury found pricing fixing conduct during part of the time frame – an allegation which Dow continues to deny – we are pleased that the jury recognized that the class claim was not proven," said Nancy Lamb, a spokeswoman with Dow.
"Dow believes that the jury verdict rejected the class claim and there are compelling post-trial motions that will be filed and addressed by the court," she added. "Dow is evaluating all of our options, including appeal."
Officials from the US Department of Justice did not immediately return requests for comment.
Dow is the last company defending itself against the lawsuit that was filed in 2004.
The lawsuit accused Huntsman, Bayer, BASF, Dow Chemical and LyondellBasell of fixing prices for propylene oxide (PO)-based polyether polyols, methyl di-p-phenylene isocyanate (MDI) and toluene di-isocyanate (TDI) that were purchased between 1 January 1999 and 31 December 2004.
In 2006, Bayer agreed to pay $55.3m to settle the suit's allegations against it.
In 2011, Huntsman agreed to pay $33m and BASF agreed to pay $51m. LyondellBasell managed to settle the case for nothing.
The court has approved all of the settlements, leaving Dow as the lone producer fighting the class-action lawsuit.
Some of the plaintiffs in the isocyanates litigation are themselves defendants in another price-fixing case.
In this case, the defendants used isocyanates to make polyurethane (PU) foam, which was then sold to bed and furniture makers.
In the lawsuit, the foam producers are accused of fixing prices for finished polyurethane foam.
So far, one of the foam makers has reached a settlement. Under it, Vitafoam would pay up to $15m. In settling the lawsuit, Vitafoam denied all allegations that it had done anything wrong.
The charges against foam producers Otto Bock and Plastomer were dismissed.
Valle Foam, one of Canada’s largest PU foam producers, has filed for creditor protection.
Others foam makers entangled in the lawsuit include Carpenter, Flexible Foam Products, Future Foam, FXI - Foamex Innovations, Hickory Springs Manufacturing, Leggett & Platt, Mohawk Industries, Scottdel and the Woodbridge Group.