Common sense has prevailed at the 2nd U.S. Circuit Court of Appeals in litigation over an alleged conspiracy among 16 global banks to manipulate the London Interbank Offered Rate (Libor), a key interest rate benchmark. The appeals court held Monday that price-fixing collusion among competitors is a violation of antitrust law, even if it takes place in the context of an ostensibly cooperative rate-setting process.

The 2nd Circuit’s 61-page opinion, written by Judge Dennis Jacobs for a panel that also included Judges Reena Raggi and Gerard Lynch, vacated a controversial 2013 decision in which U.S. District Judge Naomi Reice Buchwald of Manhattan tossed classwide antitrust claims because the Libor rate-setting process is collaborative, not competitive. The ruling revives the banks’ exposure to potentially billions of dollars in damages from investors who say they were victimized by artificial Libor rates.

Rate and market-rigging class actions against banks have become all the rage among antitrust plaintiffs’ lawyers, who’ve won nearly $2 billion in settlements in consolidated litigation over alleged tampering with the market for credit default swaps and hundreds of millions of dollars in settlements tied to manipulation of foreign exchange benchmarks. The 2nd Circuit’s Libor decision will only make the class action bar more excited about claiming collusion in the rate-setting process.

International regulatory and criminal investigators have levied about $9 billion in fines and penalties against some of the banks involved in the Libor rate-setting process, including Barclays, Deutsche Bank and UBS. Internal documents released in government probes have shown some defendants manipulated the rate-setting process to make themselves appear more stable in the financial crisis and to give particular traders an advantage over counterparties. To derive the Libor rate, banks would submit reports of the rate at which other banks were willing to lend them money; those rates were winnowed and averaged to come up with a daily Libor figure.

Judge Buchwald had said plaintiffs could not show their injury was tied to antitrust violations because banks did not compete with one another in the rate-setting process. The 2nd Circuit, however, said her reasoning was flawed. As sellers of securities that incorporated the Libor rate, the banks are competitors. Investors in Libor-pegged instruments, according to the appeals court, are buyers affected by the conspiracy. Plain and simple.

“Schematically, appellants’ claims are uncomplicated,” the appellate opinion explained. “They allege that the banks, as sellers, colluded to depress LIBOR, and thereby increased the cost to appellants, as buyers, of various LIBORbased financial instruments, a cost increase reflected in reduced rates of return. In short, appellants allege a horizontal pricefixing conspiracy, ‘perhaps the paradigm of an unreasonable restraint of trade.'”

The panel rejected as “immaterial” the banks’ arguments that Libor itself is not a product or a price and that the rules for setting the rate were implemented by the British Bankers’ Association, not by the banks. “The crucial allegation is that the banks circumvented the LIBOR-setting rules, and that joint process thus turned into collusion,” the 2nd Circuit said. Investors “have alleged an anticompetitive tendency: the warping of market factors affecting the prices for LIBORbased financial instruments. No further showing of actual adverse effect in the marketplace is necessary.”

The 2nd Circuit also held there’s no question that investors have raised plausible claims of a conspiracy so their case can’t be dismissed as inadequately pleaded. “Close cases abound on this issue, but this is not one of them,” the opinion said. “These allegations evince a common motive to conspire – increased profits and the projection of financial soundness – as well as a high number of inter-firm communications, including Barclays’ knowledge of other banks’ confidential individual submissions in advance.”

The one sliver of hope for the banks in the appellate opinion is a remand to Judge Buchwald to determine whether investors in Libor-pegged financial instruments are the right plaintiffs to enforce antitrust law. As the panel pointed out, plaintiffs have to meet two requirements to establish antitrust standing: They have to show an antitrust injury and they have to show that they are “efficient enforcers.” Judge Buchwald never reached the second issue in her 2013 decision. Now she will have to decide what the 2nd Circuit called “a closer call” than the question of whether investors properly claimed an antitrust injury.

The banks, taking a cue from the appeals court, will doubtless argue on remand that governments around the world are already punishing them for Libor transgressions. “There are many other enforcement mechanisms at work here,” the appellate opinions said. “This background context bears upon the need for appellants as instruments for vindicating the Sherman Act.”

And even the 2nd Circuit agreed that private litigation may turn out to be a bust if, for instance, “the corrupted LIBOR figure on competition was weak and potentially insignificant, given that the financial transactions at issue are complex, LIBOR was not binding, and the worldwide market for financial instruments – nothing less than the market for money – is vast, and influenced by multiple benchmarks.”

Nevertheless, the 2nd Circuit opinion answers a question about benchmark rates and antitrust claims that has divided trial judges in federal court in Manhattan. At least one of Judge Buchwald’s colleagues followed her reasoning, in a 2014 opinion dismissing a case alleging manipulation of Japanese yen Libor. But, as I’ve written, Judges Lorna Schofield and Jesse Furman squarely rejected Judge Buchwald’s interpretation of antitrust injury in more recent decisions. Schofield and Furman, in cases involving supposed tampering with the foreign exchange and ISDAfix benchmark rates, took care to distinguish the facts the in class actions before them from the Libor allegations. In particular, they emphasized that the forex and ISDAfix rates were determined through actual trades, not just by banks’ voluntary submissions.

They also, however, said Judge Buchwald had misread U.S. Supreme Court precedent to reach her conclusion. In Monday’s opinion, the 2nd Circuit agreed. The important cases to consider, the 2nd Circuit said, are 1940’s U.S. v. Socony Vacuum Oil, the seminal ruling on the per se illegality of horizontal price-fixing schemes; and 1982’s Blue Shield of Virginia v. McCready, which said consumers can sue over supposedly collusive schemes that ended up costing them money.

Investors in the various Libor classes had to go to the U.S. Supreme Court to win the right to bring an interlocutory appeal of Judge Buchwald’s antitrust decision to the 2nd Circuit. Thomas Goldstein of Goldstein & Russell, who won the Supreme Court case, argued for plaintiffs at the appeals court as well. (It took an additional nine pages to list all of the plaintiffs’ firms and amici involved in the 2nd Circuit appeal.) Robert Wise of Davis Polk & Wardwell, who argued at the 2nd Circuit for all of the banks, declined to comment.