Biddeford officials say an unknown person is impersonating a police sergeant and threatening to arrest people unless they pay him off.

An unknown person has “spoofed” the police department’s phone number and is making calls to Maine residents that appear to come from Biddeford police. The male caller then identifies himself as a sergeant, claims to have a warrant for the victim’s arrest and demands a “substantial” amount of money via gift cards, cashier’s check or Bitcoin, according to Biddeford police.

The scammer has previously claimed to be Biddeford Sgt. Philip Greenwood, but police warn he may identify himself by another name in the future.

“The Biddeford Police Department would never call you and demand cash payment to prevent your arrest,” Deputy Chief JoAnne Fisk said in a statement. “If you receive a call from anyone claiming to represent law enforcement that seems threatening or out of the ordinary, please report it to your local police department.”