The U.S. Justice Department will sue Maricopa County Sheriff Joe Arpaio if he continues to refuse to cooperate with a civil rights investigation, according to a letter obtained by The Arizona Republic.

Letter from Justice Department

The Department of Justice Civil Rights Division since March 2009 has been investigating Arpaio's operation for alleged discrimination and for unconstitutional searches and seizures. Arpaio has said he believes the investigation is politically motivated.

In a letter sent to Arpaio today, Assistant Attorney General Thomas Perez gave the Sheriff's Office until Aug. 17 to cooperate with the investigation, and to turn over documents requested last year for an inquiry into claims of discrimination based on national origin.

"MCSO's refusal to cooperate fully with the Division's investigation makes it an extreme outlier when compared with other recipients of federal financial assistance, which have uniformly recognized their obligation to cooperate with the Division's investigations of alleged discrimination," Perez wrote.

"Although we would prefer voluntary compliance in this case as well, we will not hesitate to commence litigation after Aug. 17, if MCSO continues to take the position that it need not cooperate with the Division's investigation."