Updated

The sheriff's department has developed a remarkably effective — and controversial — way of catching illegal immigrants: Deputies in patrol cars pull up to a construction site in force, and watch and see who runs.

Those who take off are chased down and arrested on charges such as trespassing, for cutting through someone else's property, or loitering, for hiding out in someone's yard, or reckless driving, for speeding off in a car.

U.S. immigration authorities are then given the names of those believed to be in this country illegally.

? Monitor the disorder on the border at FOXNews.com's Immigration Center.

"It's not wrong for them to run, but it's not wrong for us to chase them either," said Sheriff Frank McKeithen, who created his Illegal Alien Task Force in April to target construction sites in this Florida Panhandle county.

Immigrant advocates say the technique is repugnant, and the ACLU says its constitutionality is questionable.

Illegal immigrants are leaving town. And builders are worried the crackdown will deprive them of the labor they need to take part in a building boom in which Panama City's Beach cheap spring-break motels are being torn down and replaced with high-rise condos.

The sheriff said the raids are justified under a long-standing Florida law prohibiting employers from knowingly hiring illegal immigrants.

His department has conducted dozens of these raids over the past three months, sometimes using five or six patrol cars, and has reported more than 500 people to immigration officials since November.

The Mexican American Legal Defense Fund is investigating the arrests because "the intimidation factor is of great concern," said Elise Shore, regional counsel for the organization.

Benjamin Stevenson, an attorney with the American Civil Liberties Union in Florida, said he finds the tactic troubling.

"Why are they sending out six or seven agents to investigate a paper crime, and are they causing them to run in the first place through intimidation?" he asked.

As the debate over illegal immigration plays out in Washington, McKeithen is among a growing number of state and local officials taking it upon themselves to enforce immigration laws that up to now were regarded as a federal responsibility.

For example, Farmers Branch, Texas, is trying to prohibit apartment rentals to illegal immigrants in the Dallas suburb. Georgia passed a law requiring employers to verify the immigration status of all new employees.

Barbara Gonzalez, a spokeswoman for U.S. Immigration and Customs Enforcement in Miami, would not comment on the sheriff's tactics.

McKeithen has asked Florida Attorney General Bill McCollum for a legal opinion on his tactics. A spokeswoman for McCollum said the office is researching the request.

McKeithen is already under fire from civil rights groups over the videotaped 2006 death of a 14-year-old boy who was roughed up by guards at a juvenile boot camp operated by the sheriff's department. Eight former employees are facing manslaughter charges.

The sheriff said that more recently, his officers have been making fewer arrests of workers who flee, and are concentrating more on asking employers for the paperwork on their employees. Sheriff's deputies then arrest workers whose documents are found to be fraudulent.

Mexican illegal immigrant Jose Madrid, 28, said he has been unable to find a construction job over the past six weeks because of the crackdown, and hasn't been able to send money to his parents and his 7-year-old son back home.

"We immigrants, we are leaving Panama City. People are afraid they will be deported," he said. "The companies don't want to hire illegal people. Now they're only hiring those with papers."

Developer Louis Breland is finishing the first phase of a $750 million beach condo project.

"Subcontractors could not function without immigrant laborers for painting, rebar and steel work. They are the best workers," he said. "Without them, the cost of construction would be 10 times as much and nothing would get built."

Visit FOXNews.com's Immigration Center for complete coverage.