LINCOLN, Neb. (AP) — An attack that sent nine Nebraska prison employees to the hospital is ramping up pressure on state officials to increase staffing levels at their facilities.

The assaults prompted several state lawmakers to call for more manpower in the prisons. A Department of Correctional Services staffing analysis released Thursday says the agency needs to fill an additional 138 positions. The greatest need is at the Lincoln Correctional Center, which needs 44 additional positions.

Gov. Pete Ricketts on Thursday called for the state’s public employee union to negotiate immediately on a special prison employee contract.

Mike Marvin, executive director of the Nebraska Association of Public Employees, says the union cannot legally negotiate for prison employees alone. The negotiations must also include protective service staffers in the Department of Health and Human Services.