Native Americans and supporters protesting the name and logo of the Washington Redskins are seen before the game on Dec. 28 near FedEx Field. (Toni L. Sandys/The Washington Post)

The Native Americans fighting the Washington Redskins over the team’s trademark protections in a federal lawsuit got an important boost Friday when the Justice Department declared that it would intervene in a key aspect of the twisted legal case.

Dana J. Boente, U.S. attorney for the Eastern District of Virginia, filed a notice in the lawsuit on Friday that the Justice Department would defend the constitutionality of a key provision of the Lanham Act, which bars trademarks that may disparage or bring people into “contempt or disrepute.”

The Redskins sued the Native Americans in August after the group won a major decision by a U.S. Patent and Trademark Office’s appeal board. The panel ruled that the football team’s name and logo offends a substantial number of Native Americans in violation of the Lanham Act and that the team should be stripped of its trademark protections.

In its lawsuit against the Native Americans, the team has argued that the Lanham Act is “unconstitutionally vague” and that it “effectively chills First Amendment free speech rights.”

“The Redskins [trademarks] are extraordinarily powerful and valuable communicators of information, embodying in a single word of two-word phrase the entirety of the Redskins long history and rich tradition,” the team complaint says. “[The patent office appeals board] penalizes the Redskins for communicating to the public based on their marks’ content.”

Dan Snyder, the team’s owner, has promised that he will never change the name, which he says honors Native Americans. A voice message left for the team’s attorney did not receive an immediate response.

In a statement, the Justice Department said it is allowed to intervene in any “federal action in which the constitutionality of an act of Congress is drawn into question.”

“The Department of Justice is dedicated to defending the constitutionality of the important statute ensuring that trademark issues involving disparaging and derogatory language are dealt with fairly,” said Acting Assistant Attorney General Joyce R. Branda. “I believe strongly in the rights of all Americans to celebrate and maintain their unique cultural heritage. Going forward, we will strive to maintain the ability of the United States Patent and Trademark Office to make its own judgment on these matters, based on clear authorities established by law.”

Jesse Witten, an attorney for the Native Americans, said in a statement, “We are very pleased that the Department of Justice is intervening on our side.”

But the Redskins have argued in the team lawsuit that the Native Americans failed to meet a key requirement under the Lanham Act. The team contends that trademarks must be considered disparaging at the time of registration for the Lanham Act to be rightfully invoked. The team argues that not enough evidence was presented to the patent office’s Trademark Trial and Appeal Board proving that a substantial number of Native Americans were offended by the Redskins name when the team got its trademarks, between 1967 and 1990.

The dispute between the team and Native Americans has been raging for decades, but intensified in June when the trademark appeal board ruled that the team should be stripped of its trademark protections.

During this year’s NFL season, two major protests at Redskins games, in Minnesota and at FedEx Field, were led by Amanda Blackhorse, the main defendant in the team’s lawsuit.

On Friday, she welcomed the Justice Department’s support.

“I am very happy to hear they will uphold the law,” she said. “It is good to know our voice is being heard, and, indeed, this will signal to others that support for Native people continues to grow.”