Federal authorities have told a high-profile Arizona sheriff that they will investigate his department over allegations of discriminatory practices and unconstitutional searches and seizures.

The U.S. Justice Department said in a letter delivered Tuesday to Maricopa County Sheriff Joe Arpaio that the investigation will focus on alleged patterns of discrimination based on a person's national origin.

Arpaio told The Associated Press that he will cooperate with the Justice Department.

Arpaio, who describes himself as "America's Toughest Sheriff" and is best known for feeding jail inmates green bologna sandwiches, clothing them in pink underwear, and making them work on chain gangs, received praise for his anti-immigration efforts from many who believe the federal government isn't doing enough to remove people in the U.S. illegally.

But his raids and sweeps of illegal immigrants in Phoenix and nearby Guadalupe have drawn protests from community leaders and civil liberties advocates. Arpaio, a Republican, has also been criticized for letting thousands of felony warrants go unserved while he chased illegal immigrants.

According to the Arizona Department of Public Safety, there are about 59,000 outstanding, unserved felony warrants in the state. The majority are in Maricopa County, the state's most populated county.