In this Nov. 25, 2013 file photo, people carry signs protesting the Redskins name outside of FedEx Field. (Evelyn Hockstein /For The Washington Post)

In a major decision that could bolster the Washington Redskins’ legal defense of its name, a federal appeals court said Tuesday that the U.S. government can’t ban offensive trademarks, arguing that the practice violates the First Amendment.

The ruling by the U.S. Court of Appeals for the Federal Circuit in Washington came in a case involving an Asian American rock band called the Slants. The U.S. Patent and Trademark Office had rejected a trademark for the Oregon-based musicians because it considered its name a slur. But the majority of the 12-judge court concluded that no matter how disparaging the band’s name may be to Asian Americans, the First Amendment still protects the musicians’ speech — “and the speech of other trademark holders.”

The court’s decision is a significant boost to the Redskins in the team’s battle to defend its own trademark protections. In July, a federal judge in Alexandria ordered the cancellation of those trademarks — a decision the team is fighting. The judge had affirmed an earlier ruling by the Trademark Trial and Appeal Board that the NFL team’s name denigrated Native Americans and was therefore ineligible under the decades-old Lanham Act, which prohibits trademark protection for offensive names.

But the overwhelming majority of the 12-judge appeals court said Tuesday that a key provision of the 1946 Lanham Act is unconstitutional.

“Whatever our personal feelings about the mark at issue here, or other disparaging marks, the First Amendment forbids government regulators to deny registration because they find the speech likely to offend others,” the court’s opinion said. “Even when speech “inflict[s] great pain,” our Constitution protects it “to ensure that we do not stifle public debate.”

The Washington Redskins attorney, Lisa Blatt, said she was pleased with the court’s ruling but declined further comment.

The team is suing a group of five Native Americans challenging its trademark registrations. The Native Americans, led by Amanda Blackhorse of the Navajo Nation, petitioned the trademark appeal board because they asserted that “Redskins” is a slur and deeply offensive.

Jesse Witten, the Native Americans’ attorney, declined to comment on the new appeals court ruling Tuesday.

The decision could affect the team’s case before the U.S. Court of Appeals for the 4th Circuit in Richmond, where the ACLU and noted First Amendment attorney Floyd Abrams have filed amicus briefs supporting the Redskins. In its own brief, the team generated a stir by listing the names of porn, clothing and beer companies that use offensive language but nonetheless have the support of the patent and trademark office.

“By way of example only, the following marks are registered today: Take Yo Panties Off clothing; Dangerous Negro shirts . . . Midget-Man condoms and inflatable sex dolls,” the Redskins’ attorneys wrote last month. They later added a footnote with 31 more trademark registrations, many of them unprintable in The Washington Post. On the list: “Party With Sluts . . . Redneck Army apparel . . . Booty Call sex aids . . . Dumb Blonde hair products.”

The team’s lawsuit remains unresolved: the Native Americans must file their brief arguing their case by Jan. 14, which will prompt a brief reply from the Redskins. Oral arguments have not been scheduled.

Although Tuesday’s ruling in the Slants case has no binding effect on the Redskins’ appeal, the decision could influence the outcome, experts said.

Because the full appeals court declared that a key part of the Lanham Act is unconstitutional, the Justice Department can now ask the Supreme Court to review the Slants case and weigh in on the law’s validity, likely before the Redskins’ lawsuit is resolved in Richmond. Or the Justice Department could wait — and possibly let time expire to appeal the Slants case — and hope the Richmond appeals court rules that the Lanham Act’s provision doesn’t violate the First Amendment.

A spokesperson for the Justice Department declined to comment.

Mark McKenna, a law professor at the University of Notre Dame, said he expects the government to ask the Supreme Court to take the Slants case and make a final ruling on whether the Lanham Act’s provision violates the First Amendment.

“The Slants case ups the ante and makes it very likely the Supreme Court will take the case now that there’s been a declaration by a federal appeals court of unconstitutionality,” he said. “If there hadn’t been a Slants case, and the Redskins case had run its course in the appeals process and judges ruled the Lanham Act was constitutional, then it might not have ever gotten to the Supreme Court. Now it’s almost a guarantee the Supreme Court is going to take it.”