NEW BEDFORD, Mass. -- Federal investigators said the demands of $91 million in government contracts prompted a New England leather company to hire hundreds of illegal immigrants.

WCVB-TV reported Tuesday that the company was raided at 8:30 a.m. It involved hundreds of local, state and federal agents. They moved in on the Michael Bianco Inc. in New Bedford, where officials said 66 percent of the workforce was made up of illegal immigrants working in what they described as a turn-of-the-century sweatshop.

"These are the deplorable conditions that these workers essentially had to endure under," U.S. Attorney Michael Sullivan said.

"The bathrooms that I went into were very dirty. There was a lot of squalor," said Bruce Foucart of the Immigration and Customs Enforcement.

Since 2001, the plant that manufactured leather goods has won more than $90 million in defense contracts. It went from 85 employees to more than 500.

Agents arrested company owner Francesco Insolia, of Pembroke, and managers Dilia Costa, Ana Figueroa and Gloria Melo. They were all charged with conspiring to hire illegal immigrants.

Officials said the 11-month investigation was based on an anonymous tip. An undercover immigration agent posing as an illegal immigrant then secured a job at the plant and was provided with fraudulent documents.

"While working at MBI, the ICE undercover agent confirmed that many other aliens were working illegally at the company with the company's management knowledge," said Julie Myers of the Immigration and Customs Enforcement.

Aside from the terrible conditions, Sullivan said the company paid low wages with no benefits and had a system of unreasonable fines for workers.

"There was a huge economic benefit from the employer's perspective to hire undocumented immigrants," Sullivan said.

Officials said the majority of the undocumented workers are women, who will be released for humanitarian reasons pending deportation if they are the primary caregivers to children. They will also be provided with cell phones to contact their families and an attorney.