The US Department of Justice will intervene in the court battle over whether the NFL's Washington Redskins should be able to trademark their name.
The club has been under pressure from Native American groups who argue the name is offensive.
The Department of Justice said on Friday it was intervening in the case to fight the claim that the Lanham Act, which is preventing the trademarks, is unconstitutional.
"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 Joyce Branda, acting assistant attorney general for the department's Civil Division.
The case pits Pro-Football Incorporated, parent company of the Redskins, against Amanda Blackhorse et al.
It started in 2006, when Blackhorse and four other Native Americans sought the cancellation of six Washington Redskins trademark registrations under the Lanham Act, a federal law that outlaws false advertising.
They claimed the trademarks were disparaging to Native Americans, and a Trademark Trial and Appeal Board panel agreed, issuing a decision in June of 2014 that the registrations should be cancelled.
Pro-Football, then went to court, challenging the legality of the Lanham Act saying it violated First Amendment free-speech rights.
Branda said the concern of the Department of Justice in the case was 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."
Opponents of the moniker have pursued other efforts to pressure team owner Dan Snyder to change the name.
The Washington Post newspaper's editorial board said in August it would no longer use the nickname.
In September, the Change the Mascot coalition wrote to 31 owners of NFL franchises telling them they had the power to force Snyder to make a change and dozens of US lawmakers have gone on record as favouring a change.
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