According to ICE, that it is tougher to build a criminal case proving that an employer knowingly hired an undocumented than to prove that an immigrant is here illegally. The article explains that the burden of proof is on federal prosecutors to show that the employers knowingly and willingly hired undocumented immigrants.

In a statement, the immigration agency said that "the presence of illegal aliens at a business does not necessarily mean the employer is responsible," adding: "Developing sufficient evidence against employers requires complex, white-collar crime investigations that can take years to bear fruit."

Federal prosecutors often take years to put together cases against employers.

Critics say immigration officials should not allow employers to hide behind legal loopholes.

"Once again the federal government has it backwards," said Rep. Ted Poe, R-Humble, a former state judge and prosecutor. "It is a waste of time if we don't go after the business owners who are knowingly hiring illegals.

"If we eliminate the illegal job opportunities, we can start to eliminate the problem."

Earlier in the year, Homeland Security promised to crack down on employers hiring undocumented immigrations. However, there actions continue to speak louder than words. After the biggest immigration raid in US history last month in Iowa, ICE still has not charged the owners of Agriprocessors Inc.