CAMBRIDGE, Mass. — A U.S. Senate candidate is suing the city of Cambridge, saying officials violated his First Amendment rights by demanding he remove a sign from a campaign bus that read: "Only a REAL INDIAN Can Defeat the Fake Indian."

Shiva Ayyadurai, who was born in India, is running as an independent against Democratic Sen. Elizabeth Warren.

The slogan refers to claims Warren has made about Native American ancestry. It appears with an image of Warren that someone manipulated to show her in a Native American headdress.

The federal lawsuit filed April 22 says the Cambridge building inspector told the campaign it didn't have permission to display the banner on the bus that is parked at a building Ayyadurai owns, and warned of daily fines of up to $300.

The city hasn't commented on the suit.