Talk about a birthday celebration. Just before the Dallas-based company began celebrations for its 85th birthday with Free Slurpee Day, a baby named Cais Malley, nicknamed "Big Gulp," was born at a 7-Eleven in Florida. Reuters

7-Eleven might be one of the largest chains in America but some of their stores have been harboring a major secret: At least 50 of their employees are illegal immigrants. According to Businessweek, the franchise was referred to as a "modern day plantation" by federal prosecutors.

Homeland Security raided 14 7-Eleven convenience stores Monday in Long Island, N.Y., and Virginia, Reuters reported. Nine owners and managers were charged with employing unauthorized immigrants and identify theft in what is being called the biggest raid in criminal immigration forfeiture in Department of Homeland Security history, the news site reported.

According to two indictments that were revealed on Monday, eight men and one woman are charged with forcing dozens of immigrants to live in substandard housing, seizing their wages and giving them stolen identities. Businessweek said six of the accused were U.S. citizens, two were Pakistani nationals and one was from the Philippines.

"These defendants ruthlessly exploited their immigrant employees, stealing their wages and requiring them to live in unregulated boarding houses, in effect creating a modern day plantation system," U.S. Attorney Loretta Lynch of the Eastern District of New York said in a statement released with Homeland Security and the Social Security Administration, according to Reuters.

Since the workers were here illegally, it is believed they feared to report that their bosses were mistreating them. According to Homeland Security and the Social Security Administration, identities were stolen from 25 people, including the deceased and children.

7-Eleven Headquarters says it was unaware of the scheme. The company, owned by the Japanese Seven & I Holdings (Tokyo:3382), said it was working with authorities. “7-Eleven, Inc. will take aggressive actions to audit the employment status of all its franchisees’ employees,” spokeswoman Margaret Chabris said in an email to Businessweek. The company “is taking steps to assume corporate operation of the stores involved in this action so we can continue to serve our guests.”

The accused reaped millions by exploiting their workers, New York State Police Superintendent Joseph D'Amico told Reuters, and forced them to live in housing that owned by their employers, which left the victims “completely beholden” to them.

Search warrants for 30 other 7-Elevens have been granted and the probe may spread outside of Virginia and New York, investigators said.

If the nine defendants, who were charged with conspiring to commit wire fraud, stealing identities and concealing and harboring illegal immigrants, are convicted they could each face 20 years in prison.