The California Department of Corrections and Rehabilitation sterilized almost 150 female inmates without required state approvals, according to The Center for Investigative Reporting (CIR).

Doctors reportedly under contract at the prison sterilized inmates from 2006 to 2010. The CIR reports from 1997 to 2010, the state paid doctors $147,460 to perform the sterilization, according to a database of contracted medical services for state prisoners.

An estimated 148 women were sterilized, violating the prison rules during those five years, and allegedly 100 more surgeries happened during the late 1990s, according to the CIR.

Women were reportedly signed up for the surgery while pregnant and housed at the California Institution for Women in Corona or Valley State Prison for Women in Chowchilla, which is now a men's prison facility.

According to the CIR, "former inmates and prisoner advocates maintain that prison medical staff coerced the women, targeting those deemed likely to return to prison in the future."

Crystal Nguyen, a 28-year-old former Valley State Prison inmate, told the CIR she heard medical staff asking inmates who had served multiple prison terms to agree to be sterilized.

"I was like, 'Oh my God, that's not right,' " Nguyen, who worked at the prison infirmary during her time as an inmate, said. "Do they think they're animals, and they don't want them to breed anymore?"

Christina Cordero, 34, another former inmate who spent two years in prison for auto theft told the CIR the prison's OB-GYN, Dr. James Heinrich, pressured her into getting the tubal ligation before she delivered her son in 2006.

"As soon as he found out that I had five kids, he suggested that I look into getting it done. The closer I got to my due date, the more he talked about it," Cordero said. "He made me feel like a bad mother if I didn't do it."

Henrich denied pressuring any women to get the tubal ligation, according to the CIR.  He said it was important to provided the service to "poor women who faced health risks in future pregnancies because of past cesarean sections." The physician told the CIR the $147,460 cost was not a high amount.

"Over a 10-year period, that isn't a huge amount of money," Heinrich said.  "Compared to what you save in welfare paying for these unwanted children - as they procreated more."

To read more about CIR's investigation of the California prisons, click here.