The Supreme Court of the United States rejects the challenge to the class action status of a collusion lawsuit.

The Supreme Court of the United States on Monday declined to hear the Bank of America and seven other major financial institutions’ request to prevent American cities from joining a $12 billion class action lawsuit accusing them of artificially inflating interest rates on a popular municipal bond.

The judges rejected the appeal by the banks after a lower court upheld a judge’s decision to certify the action brought by Baltimore, Philadelphia, San Diego, and other cities as a class action. The Supreme Court’s decision paves the way for the lawsuit to proceed as a class action.

The cities allege that the eight banks colluded between 2008 and 2016 to raise rates on thousands of long-term variable-rate bonds. Barclays, Citigroup, JPMorgan Chase, and Goldman Sachs are among the implicated banks.

The bonds come with short-term rates that are typically reset weekly. The cities argue that the banks artificially raised interest rates, reducing available municipal funding for hospitals, schools, and other services. The banks argued in federal court in Manhattan that cities should sue for damages individually, not as a group, and denied any wrongdoing.

In their appeal, the banks argue that U.S. district judges must first resolve disputes between third-party experts on whether common issues dominate before allowing cases to proceed as class actions. They claim that the Second Circuit Court of Appeals in New York was wrong last year to confirm the certification of a national class of municipal bond issuers.

The banks told the Supreme Court that the Second Circuit’s decision, if left intact, would encourage overly broad class actions, significantly increasing potential liability and pressuring towards settlements. The cities and other municipal issuers countered that the banks were trying to turn class certification into a mini-trial on the merits of the lawsuit.

The plaintiffs also argued that there was no conflict between the appellate courts and that decisions on class certification should first focus on whether common issues can be resolved at the class level, not on whether the plaintiffs will ultimately prevail.