(AP) Wal-Mart Stores Inc., the world's biggest retailer, has agreed to pay $11 million to settle federal allegations it used illegal immigrants to clean its stores, attorneys in the case said Friday.

The landmark settlement was expected to be announced by federal immigration officials at a news conference Friday morning.

Since 1998, federal authorities have uncovered the cases of at least 250 illegal immigrants who were employed by janitor contracting services and hired by the giant retailing chain in 21 states. Many of the janitors — from Mexico, Russia, Mongolia, Poland and a host of other nations — worked seven days or nights a week without overtime pay or injury compensation, said attorney James L. Linsey. Those who worked nights were often locked in the store until the morning, Linsey said.

"We're happy that Wal-Mart may finally be putting this shameful chapter to rest with the federal authorities and we expect them not to focus on the people who were shamefully exploited from around the world," said Linsey, who is representing the workers in a civil suit against the company that is still pending in New Jersey.

The $11 million settlement clears Wal-Mart of federal allegations of hiring the illegal immigrants. Federal officials refused immediate comment Friday morning, as did Wal-Mart officials.

Wal-Mart, which has 1.2 million domestic workers, had pledged its cooperation in the investigation. Wal-Mart is based in Bentonville, Ark.

On Oct. 23, federal agents raided 60 Wal-Mart stores across 21 states, netting the alleged illegal aliens working in the stores. Almost all the workers were in the employ of subcontractors paid to clean the stores. About 10 of the workers were employed by Wal-Mart.

Officials said at the time of the raids the investigation involved wiretaps that revealed Wal-Mart executives were aware that the subcontractors used illegal workers.

The U.S. Immigration and Customs Enforcement bureau said the workers came from 18 different nations, including 90 from Mexico, 35 from the Czech Republic, 22 from Mongolia and 20 from Brazil.

Once the raid began, Wal-Mart told its executives to preserve documents. Federal agents didn't wait and moved into part of the company's Bentonville headquarters, taking boxes from the office of a mid-level executive.

Wal-Mart had begun about a year before the October raids to move toward using its own workers to clean the floors. The company said it had used more than 100 third-party contractors to clean more than 700 stores nationwide.

An employer can face civil and criminal penalties for knowingly hiring illegal immigrants or failing to comply with certain employee record-keeping regulations.

Wal-Mart Stores had sales last year of $288.19 billion.