Its board includes executives from some of the nation’s biggest companies, including Ford, Verizon, Lockheed Martin, Viacom and GlaxoSmithKline.

On the center’s 30th anniversary in 2007, Carter G. Phillips, who often represents the chamber and has argued more Supreme Court cases than any active lawyer in private practice, reflected on its influence. “I know from personal experience that the chamber’s support carries significant weight with the justices,” he wrote. “Except for the solicitor general representing the United States, no single entity has more influence on what cases the Supreme Court decides and how it decides them than the National Chamber Litigation Center.”

A study prepared by the Constitutional Accountability Center, a liberal group, examined the center’s success rate in the Supreme Court. It found that the positions supported by the chamber prevailed 68 percent of the time in the Roberts court, compared with 56 percent in the last 11 years of the Rehnquist court, a period without changes in the court’s membership. Robin S. Conrad, executive vice president of the chamber’s litigation unit, said the center’s analysis was flattering but superficial, and she questioned its comparisons.

The chamber does not participate in all business cases, she said. The mix of cases before the court has changed over time. And the chamber has become more active. But Ms. Conrad acknowledged her group’s exceptional track record. “Why have we been successful?” she asked. “I’d like to think it’s because of the quality of the arguments and the briefs we present to the court.”

“The court is looking for reliable voices to confirm its decisions, and I’d like to think it’s looking to the chamber because it tells a straight story, and we try not to be shrill or ideological,” Ms. Conrad said. “The chamber has earned a reputation for being a credible voice of business.”

Doug Kendall, president of the Constitutional Accountability Center, drew a different conclusion, saying the numbers proved that the Roberts court increasingly sided with corporate interests. He also said the study documented “a sharp ideological divide that did not exist before 2005.” In the last 11 terms of the Rehnquist court, the five more conservative justices voted for the chamber’s position 61 percent of the time, while the four more liberal justices voted for it 48 percent of the time.

In the first five terms of the Roberts court, the corresponding bloc of five more conservative justices voted for the chamber’s position 74 percent of the time, and the four more liberal justices 43 percent of the time.