PHOENIX -- Phoenix Mayor Phil Gordon has asked the FBI to investigate whether Maricopa County Sheriff Joe Arpaio's crackdown on illegal immigrants has violated any civil rights laws.

In a letter dated April 4 to U.S. Attorney General Michael Mukasey, Gordon said his request "is based on Sheriff Arpaio's pattern and practice of conduct that includes discriminatory harassment, improper stops, searches and arrests."

Gordon wrote that "over the past few weeks, Sheriff Arpaio's actions have infringed on the civil rights of our residents."

Gordon said Arpaio should be investigated based on four laws -- the Civil Rights Act of 1964, the Violent Control and Law Enforcement Act of 1994, the Omnibus Crime Control and Safe Streets Act and a "color of Law" violation.

Arpaio lashed back at the mayor on Sunday. The sheriff said Gordon wrote the letter for political reasons.

"Because we've been doing this for two years and haven't had any problems until I went into his city because his police will not enforce the laws and he does not want me to lock up illegals," Arpaio said.

Sheriff's deputies and trained volunteers have taken to the streets in recent weeks stopping motorists for routine traffic violations and in some cases asked them about their immigration status, Gordon noted in his letter.

The mayor also cited Arpaio's crime "saturation patrols" in certain neighborhoods launched at the request of business owners who complained of rising crime.

Gordon noted the most recent sweep in Guadalupe. He said the town usually ranks near or at the bottom of violent crime.

"His expansion of these roundups, with no end in sight, has compelled me to write this letter today," Gordon said.

Recently, several other groups have denounced MCSO's sweeps. They include the Arizona chapter of the Anti-Defamation League, the Arizona Ecumenical Council and American Jewish Committee.