The Arizona correctional officers union said Monday that they're worried the sexual assault of a guard shows that prison understaffing has created a safety threat.

A spokesman for the Arizona Correctional Peace Officers Association said Corrections Department Director Charles Ryan has made the problem worse by firing officers when lesser punishments are possible.

"We're concerned about staffing, which always comes into play: short staffing," spokesman Robert Blackmer said. "We certainly call on the management to make some serious efforts to protect all the employees because staff assaults are at a record high."

It isn't clear if understaffing played a role in the April 13 attack at the state prison complex in Yuma. It was the second sexual assault on a state prison employee in the last 18 months.

The Department of Corrections acknowledged the assault by an inmate with a history of violence late Friday.

The guard was meeting with inmate Fernandes Masters, 31, in a housing unit office when he attacked her, Corrections spokesman Andrew Wilder said. Masters was eventually stopped by other guards, he said.

The department plans to seek sexual assault, kidnapping and attempted murder against Masters, was convicted of killing his stepfather in 2004 while robbing him to get money for drugs. He is serving a life sentence.

Masters' lawyer has not returned calls seeking comment.

An investigation is ongoing, and Wilder couldn't say whether any prison policies were violated or if a policy review is being considered.

Blackmer said the inmate choked the female guard and was removing her clothes when other officers intervened. She has not been identified but is a union member.

The woman was a Corrections Officer 3, a post that essentially acts as a counselor for prisoners, Blackmer said.

The assault follows the January 2014 rape of a female teacher at another prison that brought intense criticism of the Arizona prison procedures for safeguarding corrections workers. The teacher is suing corrections officials for failing to protect her. She was alone in a classroom giving assessment tests to inmates in a sex offender unit at the Eyman prison in Florence when she was attacked.

Chronic understaffing has long been a problem in Arizona's prisons. Exact staffing levels weren't immediately available Friday, but the agency's 2016-2020 strategic plan said it is a major problem with no easy solution.

Issues cited in the report include low pay, generational issues with differing expectations about technology and work ethic and challenging labor laws.

"Despite the success of improved recruitment efforts, staffing shortages have increased," the plan said. "One thousand Correctional Officers were hired in Fiscal Year 2014, yet the vacancy rate climbed as a result of challenges with retention. ADC continues to lose staff due to the adverse environment, non-competitive pay, and the increasingly physical nature of confrontations with inmates."

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