PHOENIX (AP) -- Federal authorities sued America's self-proclaimed toughest sheriff Thursday after months of negations failed to yield an agreement to settle allegations that his department racially profiled Latinos in his trademark immigration patrols.

The U.S. Department of Justice lawsuit marked an escalation in the agency's civil rights investigation of Joe Arpaio and puts the dispute on track to be decided by a federal judge.

The DOJ first leveled the allegations against Arpaio in December, saying that a culture of disregard for basic constitutional rights prevailed at the Maricopa County sheriff's office, which covers metro Phoenix. Federal officials held off on filing a lawsuit as they tried to reach a settlement, but talks broke off last month.

At the time, Arpaio refused to agree to a court-appointed monitor who would help enforce a settlement. Arpaio said it would mean every policy decision would have to be cleared through an observer and would nullify his authority.

At a news conference Wednesday, after DOJ officials notified him of their intent to sue, Arpaio defended himself.

"If they sue, we'll go to court," he said. "And then we'll find out the real story. They're telling me how to run my organization. I'd like to get this resolved, but I'm not going to give up my authority to the federal government. It's as simple as that."

Arpaio's office is also accused of punishing Hispanic jail inmates for speaking Spanish and launching some patrols based on complaints about dark-skinned people congregating in a given area or speaking Spanish. A crime was never reported.

The DOJ has been seeking an agreement requiring Arpaio's office to train officers in how to make constitutional traffic stops, collect data on people arrested in traffic stops and assure Latinos that the department is there to also protect them.

"Constitutional policing is an essential element of effective law enforcement," according to the DOJ lawsuit. The sheriff's office "and Arpaio's conduct is neither constitutional nor effective law enforcement."

One of the examples cited in the lawsuit was a Latino woman who is a U.S. citizen and was 5-months pregnant when she was stopped as she pulled into her driveway.

When the woman refused to sit on the hood of a car as the officer insisted, the officer pulled her arms behind her back, slammed her stomach first into the vehicle three times and dragged her to his patrol car. He shoved her into the back seat and made her wait for about 30 minutes without air conditioning, the lawsuit said.

Eventually, the woman was cited for failure to provide proof of insurance, but the matter was resolved when she provided such proof to a court, the lawsuit said.

The sheriff has said the investigation was a politically motivated attack by the Obama administration, denied allegations of systematic discriminatory policing and insisted that the Justice Department provide facts to prove its allegations. The Justice Department has said a 22-page letter it sent to Arpaio in December provided those details.

Arpaio is a national political fixture who built his reputation on jailing inmates in tents and dressing them in pink underwear, selling himself to voters as unceasingly tough on crime. Along the way, he aggressively pushed for a stronger role for local police to confront illegal immigration, launching 20 patrols looking for illegal immigrants since January 2008.

During the patrols, deputies flood an area of a city - in some cases, heavily Latino areas - over several days to seek out traffic violators and arrest other suspected offenders. Over the last three years, he also raided 58 businesses suspected of breaking a state law by knowingly hiring illegal immigrants.

Earlier in the three-year investigation, the Justice Department filed a lawsuit against Arpaio, alleging his office refused to fully cooperate with a request for records and access to jails and employees. That 2010 case was settled last summer after the sheriff's office handed over records and gave access to employees and jails.

Separate from the Justice Department's allegations, a lawsuit that alleges that Arpaio's deputies racially profiled Latinos in immigration patrols is scheduled for a July 19 trial in federal court.

A federal grand jury also has been investigating Arpaio's office on criminal abuse-of-power allegations since at least December 2009 and is specifically examining the investigative work of the sheriff's anti-public corruption squad..

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