Italian American groups have filed a lawsuit in Philadelphia after the city's mayor replaced the Columbus Day holiday with Indigenous People's Day.
Officially observed since 1937, it commemorates Christopher Columbus landing in the Americas in 1492.
The city's mayor has dismissed the suit as a "political ploy".
The 36-page lawsuit filed on Tuesday in the US District Court for the Eastern District of Pennsylvania accuses Philadelphia Mayor Jim Kenney of acting "unilaterally" when he chose to rename the holiday this January.
In their complaint, the Conference of Presidents of Major Italian American Organisations, the 1492 Society, and an Italian American member of the Philadelphia City Council state: "While both groups' ethnicity deserves recognition, Mayor Kenney may not take action that discriminates against Italian Americans to exalt another ethnic group in its place.".
It also claims the mayor is "unmistakably bent on prejudicing Italian Americans" and, among other allegations, points to his role in attempting to remove a statue that is typically the centrepiece of Columbus Day festivities.
In a statement to CBS News Philadelphia, Mr Kenney dismissed the lawsuit as "a patently meritless political ploy".
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