Retailers, angered by what they considered to be too high a cap, brought suit against the Federal Reserve's rule, arguing the regulator had not interpreted the statute correctly in establishing the cap and requiring only two independent payment networks.

Leon agreed. The appeals court did not.

"The district court granted summary judgment to the merchants, concluding that the rules violate the statute's plain language," the panel wrote in its 38-page decision. "We disagree. Applying traditional tools of statutory interpretation, we hold that the board's rules generally rest on reasonable constructions of the statute."

The National Retail Federation repeated its displeasure with the March 21 decision but did not say what it will do next.

The NRF could request that all judges on the court hear the case instead of the three-judge panel. But since the panel ruled unanimously, analysts familiar with the court said it was unlikely the entire court would consider it.

Second, the retailers could appeal to the Supreme Court, but absent any notable legal conflicts, such as having two conflicting rulings, the high court is seen as unlikely to take it up.

Finally, retailers could ask for a retrial in district court. While a real possibility, the experts said, any new case would take place in the light of the upper court's ruling which directly attacked the retailers' central arguments, making a victory there unlikely.

"Theoretically, the merchants have options on how to next proceed," wrote Brian Gardner, an analyst with Keefe, Bruyette and Woods. "However, as a practical matter, we do not think these options are good ones for the merchants."