The Supreme Court won't hear an appeal from a group of flexible foam manufacturers challenging one of the largest class action lawsuits ever certified.

The justices on Monday let stand a lower court ruling that allowed a lawsuit to go forward that seeks more than $9 billion in damages against Carpenter Co., Woodbridge Foam Corp. and others.

Buyers of flexible foam products including seat cushions, foam pillows and mattresses allege the manufacturers were involved in a decades-long conspiracy to fix the price of polyurethane foam.

The companies claim there is not enough in common between various purchasers of the foam products to allow a class action to proceed. The 6th U.S. Circuit Court of Appeals rejected that argument.