Florida ? 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.

“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.

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

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.