A former human resources manager arrested after a massive immigration raid at an Iowa kosher slaughterhouse pleaded guilty Monday to federal immigration charges.

Elizabeth Billmeyer, of Postville, pleaded guilty to one count of conspiracy to harbor undocumented aliens for profit and one count of knowingly accepting false resident alien cards.

The 48-year-old worked at the Agriprocessors Inc. plant in Postville, once the nation's largest kosher slaughterhouse. She faces up to 20 years in prison and a $500,000 fine.

Federal agents arrested 389 people in an immigration raid at the Agriprocessors plant last May. Charges were later filed against some of the company's top managers and supervisors.

Agriprocessors also operated a plant near Gordon, Neb., that was not involved in the allegations.

According to a news release from the U.S. attorneys office, over a five-year period leading up to last year's raid Billmeyer conspired with others to harbor illegal immigrants at the plant for commercial advantage and private financial gain. She is also accused of accepting false resident alien cards knowing they were forged or counterfeit.

Besides the federal immigration charges against Agriprocessors and its managers, Billmeyer and others still face thousands of state child labor law charges.