Immigration agents arrested seven executives and hundreds of employees of a manufacturer of crates and pallets Wednesday as part of a crackdown on employers of illegal workers.

Authorities raided offices and plants of IFCO Systems in at least nine states, the culmination of a yearlong criminal investigation, law enforcement officials said.

U.S. Immigration and Customs Enforcement agents arrested seven current and former IFCO Systems managers on charges they conspired to transport, harbor and encourage illegal workers to reside in the United States for commercial advantage and private financial gain, said Glenn T. Suddaby, the chief federal prosecutor in Albany, N.Y., where some arrests were made.

ICE spokeswoman Jamie Zuieback confirmed an unspecified number of raids and arrests, but declined to provide additional details because the investigation was continuing. One official, speaking on condition of anonymity because numbers were still being tallied, said the arrests were in the hundreds.

Raids took place at several locations in upstate New York and in Biglerville, Pa., Charlotte, N.C., Cincinnati, Houston, Indianapolis, Phoenix, Richmond, Va., and Westborough, Mass.

"ICE has no tolerance for corporate officers who harbor illegal aliens for their work force. Today's nationwide enforcement actions show how we will use all our investigative tools to bring these individuals to justice, no matter how large or small their company," said ICE chief Julie Myers.

She and Homeland Security Secretary Michael Chertoff are expected on Thursday to lay out an immigration enforcement strategy that targets employers' disregard for immigration law.

Last week, operators of three restaurants in Baltimore pleaded guilty to similar immigration charges, while nine people affiliated with two temporary employment agencies that do business in New Jersey, Ohio and Pennsylvania were charged in a $5.3 million scheme involving the employment and harboring of illegal aliens.

Several immigration proposals pending in Congress would stiffen penalties against employers who hire illegal immigrants.

German-based IFCO Systems describes itself as the leading pallet services company in the United States, focusing on recycling millions of the wooden platforms used to stack and move all manner of goods. It operates about five dozen facilities nationwide and has been expanding steadily, according to the company's Web site.

IFCO Systems acknowledged that a number of employees were detained Wednesday and pledged to cooperate with the investigation.

"It is our policy to comply with all federal and state employment requirements," the company said in a statement.

In Houston, Jose Rivera, an immigrant from El Salvador, went to one of the company's Houston operations to search for information about his 22-year-old son, an IFCO Systems employee who was arrested Wednesday. Rivera said a brother, who worked at an IFCO operation in Louisiana, also was arrested Wednesday.

"I really feel angry because this is an injustice," he said through a translator. "It's an injustice because one person, who come from another country, why can't you work?"

Rivera said his son has worked for IFCO for about a year and a half.

The current and former IFCO Systems managers arrested were identified by Suddaby as: Michael Ames, 44, Shrewsbury, Mass.; Robert Belvin, 43, Clifton Park, N.Y.; Abelino Chicas, 40, Houston; Scott Dodge, 43, Albany; William Hoskins, 29, Cincinnati; James Rice, 36, Houston, and Dario Salzano, 36, Amsterdam, N.Y.

Last year, Wal-Mart stores agreed to pay $11 million to settle allegations concerning the employment and mistreatment of illegal immigrants.

Wal-Mart has maintained that top executives did not know that cleaning contractors were hiring illegal immigrants, who sometimes slept in the backs of stores. An ICE affidavit unsealed as part of that case, however, asserted that two executives were aware of the practice.