One Arizona county sheriff has created a 250-strong posse to hunt down those who cross the border illegally.
"I'm the only agency enforcing this law because it is the law," Maricopa County Sheriff Joe Arpaio told FOX News. "It's a violation of the law, and I'm going to put tents up from here to Mexico if I have to to keep these illegals incarcerated."
But Arpaio's actions are already causing some controversy.
Arpaio, the sheriff for Arizona's most populous county, is taking advantage of a new state law that allows charging undocumented immigrants with criminal conspiracy to smuggle themselves into the United States. Previous laws had made entering the U.S. illegally a misdemeanor, not a felony. The anti-human-smuggling statute took effect in Arizona in August and gave prosecutors a tool to go after "coyotes," or smugglers, who traffic in undocumented immigrants.
The Maricopa County Attorney's Office later issued an opinion saying undocumented immigrants suspected of paying coyotes could be prosecuted as conspirators.
"It’s a felony; I am enforcing a new law," Arpaio said. "I’m the elected sheriff and I'm going to do what I feel is right regardless of the controversy."
On Wednesday night, Arpaio and his posse launched patrols in desert areas and major roadways southwest of Phoenix in search of illegal immigrants to arrest. FOX News' William LaJeunesse rode along on some of the patrols.
The group was comprised of existing Maricopa County sheriff's deputies and members of the department's 3,000-member posse reserve of trained volunteers.
The posse was patrolling the area here for illegal immigrants who pay smugglers to cross through Arizona, the busiest illegal entry point along the 2,000-mile U.S.-Mexico border. There have been 147 arrests since the posse began its roundups six weeks ago, including at least one arrest Wednesday night.
The unorthodox sheriff's department has built a tent city that currently houses around 2,000, with inmates forced to wear pink underwear.
Those who are captured by the posse may end up in jail, charged under the state law that allowed local law enforcement agencies to charge suspected smugglers in Arizona — it was already a federal crime.
"I equate it to the drug traffic," Arpaio told FOX News. "I spent 38 years fighting the international drug traffic. You arrest the supplier, you arrest the customer. It's the conspiracy, the customer to buy — the same thing here.”
But local pro-immigrant activists disagree with Arpaio's tactics.
"You need to get federal training to become an immigration officer and they have not done it yet, so they are stepping out of bounds," said Hector Yturralde of "We Are America." He worries that posses like Maricopa's one could target Hispanics who live in the country legally.
"I've got brown hair, I've got brown skin, I've got dark eyes," he said, voicing concern about racial profiling. "You're going to pull me over. What happens if I don't have identification on me? As a U.S. citizen, sometimes it happens. Where am I going to end up?"
FOX News has learned the Mexican government has hired a stateside lawyer to sue Arpaio and the county over the new statute.
The federal law has been used against more than 100 illegal immigrants in Maricopa County this year. The law was meant to crack down on smugglers, but under a disputed interpretation, County Attorney Andrew Thomas argues the law also can be applied to the smuggled immigrants themselves.
Thomas maintains illegal immigrants who pay smugglers to enter the United States are committing conspiracy to smuggle and can therefore be prosecuted under the state law. It's punishable by up to two years in jail.
"It's going to be a help to the county," posse member D.J. Pigott said. "Illegal immigrants are getting everything that, in my estimation, they should not get. We're being overrun by these people. If the federal government is not going to do it, the sheriff is going to do it."
As states and localities — particularly those along the Mexican border — try to grapple with the large number of illegal immigrants coming into their areas, many complain that the federal government is not doing enough to curb the problem. But federal officials have been conducting raids to try to show they're serious about cracking down on businesses that employ undocumented workers.
Julie Myers, the assistant secretary for U.S. Immigration and Customs Enforcement (ICE), told FOX News that no business is immune from investigation.
"Follow the law," Myers said. "If you don't follow the law, you risk us coming after you, you risk having workers who are scared to show up because they think ICE might show up at their door."
She added: "We certainly understand the frustration of the American people. We share that frustration. We're working creatively to solve this problem."
It remains to be seen whether a judge will uphold the smuggling law as applicable to illegal immigrants. Lawyers for some arrested illegal immigrants have filed motions to have the charges dismissed.
The Center for Human Rights and Constitutional Law in Los Angeles is challenging Thomas's interpretation.
"We agree with Andrew Thomas that federal immigration policy is a mess," said Peter Schey, director of the human rights group. "But we part company when it comes to what should be done about that. We don't believe anyone has the right to break the law because they're frustrated with federal policy."
Even the authors of the state smuggling law say it was meant to crack down on violent immigrant smugglers — not the people they're transporting.
"I never intended that immigrants would be arrested," said Rep. Jonathan Paton, a Republican who was one of three legislators to write the smuggling law.
Other police agencies say that arresting illegal immigrants under the law would overwhelm them financially.
"I can't afford to do what Sheriff Arpaio is doing," said Sheriff Tony Estrada of Santa Cruz County, one of four Arizona border counties. "He can do a lot of crazy things with his resources. We can't. We're strapped."
FOX News' William La Jeunesse and The Associated Press contributed to this report.