Shiva Ayyadurai, an independent candidate challenging Democratic Massachusetts Sen. Elizabeth Warren in November, is suing Warren’s hometown of Cambridge for demanding that he removes signs labeling her a “fake Indian.”

Ayyadurai, who has billed himself as the “real Indian” in the race, was born in Bombay, India.

Ayyadurai’s federal lawsuit, filed Sunday, accuses the city of violating his free speech when officials ordered him to remove two campaign signs picturing Warren in a Native American headdress along with the slogan: “Only a real Indian can defeat the fake Indian.”

Another great day! Volunteers and supporters for #Shiva4Senate. pic.twitter.com/HLcfaW48vC — Dr. Shiva Ayyadurai,PhD (M.I.T.) Inventor of Email (@va_shiva) April 22, 2018

The signs were posted on the side of a bus parked on property owned by Ayyadurai, but Cambridge building inspector Branden Vigneault says they still violate city zoning ordinances. “These signs must be removed immediately. Failure to do so, may result in fines up to $300.00 dollars per day and legal action,” Vigneault said.

Ayyadurai’s suit argues that because the signs are posted on a bus rather than a building, those ordinances do not apply. He further accused city officials of attacking his campaign for political reasons. “This is a political vendetta by City officials who are supporters of Elizabeth Warren,” he claims.

Ayyadurai has long been critical of Warren’s claims to Native American heritage, and once admitted to sending the senator a DNA test for her birthday. He told Fox Business’ Stuart Varney that he was “very sad” when she opted to return the gift.

In recent months, Warren has defended her decision not to take a DNA test, insisting, “I know who I am.”