Many employees recouped more than $30,000 in back pay, benefits, overtime and holiday pay, officials said, and had worked at the lesser pay rate for up to five years.
The facility houses federal inmates being detained by the U.S. Marshal and federal immigration authorities, as well as state inmates. The back wages applied only to CCA employees working with federal inmates.
Company spokesman Jonathan Burns disputed the findings.
The company was complying with the terms of its original agreement with the correctional facility, and the Labor Department decided to retroactively apply a wage standard that wasn't part of that agreement after a compliance audit two years ago, he said. Corrections Corp. of America will seek a retroactive cost increase for the contract to absorb the additional wages and benefits, he added.
"We greatly value our employees and the important work that they do to keep our communities safe and secure," Burns said in a statement.
The company also wasn't making the required contributions to health and life insurance and retirement accounts, he said. The investigation also found record-keeping violations under the Fair Labor Standards Act, include inaccurate recording of breaks, lunches and overall hours worked.
"If somebody was supposed to be making $30 an hour, they were making $20 an hour instead," said Huerta.
"The people that get these federal monies from a federal agency to get one of these contracts have to abide by the wage rates."
Corrections Corp. of America — the fifth-largest prison system in the nation — has come under scrutiny before.
In Kentucky, it paid $260,000 last week to settle claims that it denied overtime to shift supervisors and forced them to work extra hours.
In Kansas, CCA and a group of collections officers, case managers and clerks settled in 2009 in federal court over allegations of unpaid overtime. CCA agreed to pay a maximum of $7 million but did not acknowledge fault in the case.
Idaho announced this year that it would not renew a $29 million-a-year contract with the private prison company and began the process of returning operations of the state's largest prison, in Boise, to state control.
The facility was sued and plagued by accusations of violence, gang activity and understaffing after the private prison contractor took it over.
Corrections Corp. of America operates detention centers for federal, state and local governments in 20 states in the U.S. and houses nearly 80,000 inmates at 60 facilities.
California City is about 110 miles northeast of Los Angeles.