All U.S. Supreme Court victories are big events, but one that ­revolutionizes consumer class action law? Call it the capstone to an already big year for Chicago-based Mayer Brown.

In AT&T Mobility v. Concepcion, the Court ruled, 5-4, that the Federal Arbi­tration Act pre-empted a California state law prohibiting contracts from disallowing class actions. The case involved a couple who alleged that the process of charging sales tax on a cellphone advertised as free was fraudulent. Partner Andrew Pincus argued the case.

Since the ruling in April 2011, judges have dismissed dozens of lawsuits around the country, citing Concepcion.

The firm scored a big win in the 9th Circuit in Mazza v. American Honda Motor Co. In January, the court ruled that a federal trial judge erred in certifying a nationwide class of Acura buyers under California law because the law could not be applied to the whole class. Three California residents alleged that Honda had concealed information about the model’s brakes. Partner Donald Falk presented the argument.

Concepcion and Mazza have had a major impact on the landscape for class actions. It really does require plaintiff lawyers to trim their sails,” said Supreme Court and appellate practice partner Evan Tager. “Clients have hired us throughout the history of our appellate group for the purpose of shaping and developing issues and the law by picking the right vehicle.”

Roughly 50 attorneys operate in Mayer Brown’s practice; its members have argued more than 220 cases before the Supreme Court — an average of four per term. The team handles clients regionally from its offices in New York; Chicago; Palo Alto, Calif.; and Washington. According to Tager, the practice operates “more like a web — not the solar system where there’s one star that everyone revolves around.”

Neal Berinhout, associate general counsel for AT&T Mobility, described Mayer Brown’s work as “outstanding in every respect. Their writing is spectacular and the oral argument has been outstanding.”

Paul Bland, senior attorney at Wash­ington-based public interest law firm Public Justice, who has opposed Tager in a variety of cases, paid him grudging respect. “More than 100 class actions have been thrown out since that decision [Concepcion], and it was exceptional lawyering that got them to achieve that result.”

Tager exemplifies the Mayer Brown style, he said. “He’s a good-hearted, professional and courteous person. There are a lot of lawyers at that level who behave like they’re in the NBA, but there’s nothing like that at that firm.” — Lisa Holton