A federal judge in Brooklyn has awarded $544.8 million to a group of plaintiffs attorneys who filed a class action on behalf of 12 million merchants against Visa, MasterCard, and a group of banks.

It is the largest attorney fee award granted in a private antitrust case.

Eastern District Judge John Gleeson (See Profile) gave the firms all but $25 million of the amount they requested, noting that a similar earlier case had failed, and they weren’t piggybacking on a government action.

“If not for the attorneys’ willingness to endure for many years the risk that their extraordinary efforts would go uncompensated, the settlement would not exist,” the judge wrote in his 17-page order.

The plaintiffs lawyers, who filed their litigation in 2005, were led by Robins Kaplan Miller & Ciresi, Robbins Geller Rudman & Dowd, and Berger & Montague. These three firms contributed about 55 percent of the hours in the fee request, which suggests they could split about $270 million.

In December Gleeson approved a $5.7 billion settlement resolving claims brought by merchants accusing the defendants of conspiring to fix the so-called interchange fees that retailers are charged when customers pay with credit cards.

The plaintiffs’ team asked for 10 percent of the settlement value. But Gleeson calculated the award on a graduated scale: 33 percent of the fund up to $10 million, 30 percent of the next $40 million, 25 percent of the next $50 million, and so on until granting 6 percent of the value between $2 billion and $5.7 billion. The final fee amounted to 9.56 percent of the fund.

The plaintiffs lawyers may face additional hurdles before they see their payday. The case docket is peppered with notices of appeal filed by small retailers challenging the settlement and the fee.