AUSTIN  —  Private prisons holding more than 25,000 people who violated U.S. immigration laws are cutting corners to generate profits and subjecting inmates to systematic abuse, a report released on Tuesday by the American Civil Liberties Union said.

The Criminal Alien Requirement (CAR) prisons, five of which are located in Texas and eight in other states, have drawn little attention and oversight, while subjecting inmates to “shocking abuse and mistreatment,” the report said.

“Putting profit before people seems to touch every facet of life at CAR prisons,” the report said.

“The U.S. Bureau of Prison’s reliance on private prisons is unlikely to end any time soon.”

The Bureau of Prisons (BOP) spent about $600 million in the 2013 fiscal year to pay for what it calls the “privately operated institutions,” according to the ACLU.

The bureau said it takes the allegations seriously but will not comment on the report’s specifics. It added the bureau’s low-security institutions are overcrowded and it monitors the private prisons closely.

“The bureau has found that contracting with the private sector provides an effective means of managing low security, specialized populations,” it said in a statement.

One of the three companies that run the prisons, Corrections Corporation of America did not reply to requests for comment. The two other companies, MTC and the GEO Group, denied the report’s allegations, saying their facilities are appropriately equipped and accredited.

“Our facilities adhere to strict contractual requirements and standards set by the Federal Bureau of Prisons, and the agency employs full-time, on-site contract monitors who have a physical presence at GEO’s facilities,” a statement said.

The ACLU report said the prison contract between the BOP and providers are for “low security, short-term, sentenced criminal aliens” and call for prisons to use 10 percent of their beds for isolation cells, a figure double or triple what is used in many prison systems.

This leads to the widespread use of solitary confinement for minor prison infractions, the report said.

Overcrowding is endemic, while medical facilities are not as well equipped as those offered in other prison systems, it said.

Prison operator MTC said: “The allegations that we provide poor medical care are unfounded.”

The number of immigrants entering these facilities rose sharply after new zero-tolerance immigration policies were implemented in 2005 in which many immigrants subject to deportation for violating U.S. immigration law were also referred to U.S. authorities for prosecution, it said.

The ACLU report was based on an investigation that started in 2009 and focused on the prisons in Texas. Nearly 300 detainees were interviewed and several sites visited.