(CNN) -- The Arizona sheriff who bills himself as "America's toughest" will be in a courtroom Thursday as a racial discrimination trial against his department gets under way.

Joe Arpaio is nationally known for his tough stances against illegal immigration, but critics have said for years that his approach has created a system of racial profiling.

The U.S. Justice Department has filed a civil rights lawsuit against him, but Thursday's trial is for a different lawsuit brought by Hispanics who say they were discriminated against.

The class-action lawsuit, filed in 2007, claims that Arpaio and the Maricopa County Sheriff's Office "launched a series of massive so-called 'crime suppression sweeps' that show a law enforcement agency operating well beyond the bounds of the law."

The plaintiffs are being represented by the American Civil Liberties Union and the firm Covington & Burling.

Arpaio's office did not immediately respond to a request for comment on the trial's start.

The lawsuit charges that the sheriff's office "unlawfully instituted a pattern and practice of targeting Latino drivers and passengers in Maricopa County during traffic stops," the ACLU said in a statement.

The sheriff's tactics violate the Equal Protection Act by discriminating by race and result in prolonged detentions that violate protections against unreasonable searches, the ACLU said.

The office's "pattern and practice of racial profiling goes beyond these sweeps to include widespread, day-to-day targeting and mistreatment of persons who appear to be Latino," the lawsuit states.

Among the plaintiffs is Manuel Ortega Melendres, a visitor to Arizona who possessed a valid visa. In September 2007, he was arrested after the car he was riding in was pulled over by Maricopa County deputies. The lawsuit alleges that Melendres showed the officers his identification but was nonetheless treated roughly and arrested. He sat in a cell for hours before a federal immigration agent confirmed that his documents were in order.

As a result of his ordeal, Melendres was left "frightened to walk on the street or be seen in public in Maricopa County because he fears that the sheriff's officers will come and arrest him again because he is Latino and does not speak English," the lawsuit states.

Arpaio has accused the Justice Department of playing politics.

"They're using me for the Latino vote, showing that they're doing something, taking on the sheriff over an alleged racial profiling," Arpaio said.

He vowed to defend himself not for selfish purposes but to help thousands of other sheriffs in the country avoid similar situations.

"I'm not going to surrender my office to the federal government," he said of the Justice Department lawsuit. "I will fight this to the bitter end."