UPDATE 3-Immigration arrests top 300 at Iowa meat plant

(Recasts with arrests, updates throughout, adds byline)

By Bob Burgdorfer

CHICAGO, May 12 (Reuters) - U.S. immigration agents arrested more than 300 people on Monday at Agriprocessors Inc, a kosher meat plant in Postville, Iowa, amid an ongoing investigation into identification theft, fraudulent use of Social Security numbers, and for illegal immigrants, Immigration officials said.

"This is the largest operation of this type ever in Iowa. Agents and officers from federal state, and local agencies are involved today," U.S. Attorney Matt Dummermuth said in a statement.

The investigation was led by the U.S. Immigration and Customs Enforcement (ICE) unit.

More than 40 of those arrested were later released on humanitarian grounds. Also, ICE established the toll-free number 1-866-341-3858 so that family members can call and get information regarding the custody status and detention location of those detained.

Agents began searching the plant in northeast Iowa at about 10 a.m. CDT (1500 GMT) and by Monday afternoon more than 300 had been arrested for "administrative immigration violations", according to a U.S. Department of Justice statement.

In its online edition the Des Moines Register newspaper, citing Iowa Workforce Development, reported the plant employs 1,000 to 1,050 people.

The Iowa Workforce Development website listed Agriprocessors as the state's seventh largest employer in 2006.