THE U.S. Immigration and Customs Enforcement agency has been cracking down on what it sees as what's fueling illegal immigration: Employers.

It's been doing this through a stepped-up use of the I-9 audit. The I-9 is the form that employees have to fill out to verify that they are eligible to work here.

On July 1, ICE announced that it was alerting 652 businesses nationwide that they were to face an audit of their I-9 forms. In comparison, ICE issued 503 such alerts in the entire 2008 fiscal year.

An internal ICE memo, sent in April, emphasized that "criminal prosecution of employers is a priority." The memo, since made public, said that the full range of investigative techniques should be used, including the "use of confidential sources and cooperating witnesses, introduction of undercover agents, consensual and nonconsensual intercepts and Form I-9 audits."

Kate Kalmykov, an associate who specializes in business immigration and compliance in the New York office of Klasko, Rulon, Stock & Seltzer LLP, which also has a Philadelphia office, said this stepped-up focus on employers is definitely a warning signal that ICE is "taking action."

But, most of all, she said, with about 12 million undocumented immigrants in the nation, it's a signal that "some comprehensive reform is needed."

The Philadelphia offices of ICE are responsible for the states of Pennsylvania, Delaware and West Virginia. Agents in its Office of Investigations said that they are conducting I-9 audits on companies in the area, but can't name those businesses.

The office also focuses on employers suspected of a variety of crimes, such as money laundering, human smuggling and human trafficking, and in those cases won't send any kind of notice alerting employers that they are being investigated.

The office is aware of immigrant communities' use of temporary-employment agencies to find jobs for undocumented workers. It sees such agencies as a threat.

Such agencies serve immigrants not only from Indonesia, but have cropped up to serve Hispanics from Central and South America, Africans, Chinese and Vietnamese, according to ICE.

"These temporary employment agencies act as criminal organizations," Andrew McLees, deputy special agent in charge of the Office of Investigations in Philadelphia, said in an interview in ICE's office, on Chestnut Street near 2nd, last week.

"Because their illegal activities start right up front when they hire that employee, and then they're transporting that employee to the work site, and, in some cases, they're harboring the employee, . . . the proceeds that they receive in return for providing that employee is illegal."

McLees said that the agency doesn't have the resources to go after every illegal immigrant.

"Our resources don't allow us to do that," he said. "We have to use our finite resources to focus on employers who are egregiously hiring illegal aliens. . . . We're really focused on people who are breaking the law and that we can bring to justice criminally."

One thing that the agency would like to make clear is that it doesn't go out and search for illegal immigrants at random.

Mark Medvesky, the local ICE spokesman, said: "We do targeted-enforcement operations, where when our agents and our officers go out to a location they are looking for specific people or they know that there's a specific group of people there, and it's limited to the area where they expect them to be, to the people they expect to find. It's not just a sweeping kind of action, it's very direct and targeted."