CHICAGO (CBS) — More than 2,200 nurses who went on strike last week at the University of Chicago Medical Center are headed back to work Wednesday morning.

The nurses staged a one-day strike that started last Friday, but the hospital locked them out until 7 a.m. Wednesday, saying it needed to guarantee a minimum of five days’ work to the temporary nurses it hired to fill in during the strike.

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National Nurses United represents 2,240 nurses who work at the University of Chicago Medical Center and its clinics. The nurses staged the one-day strike after contract negotiations broke down last week. After being locked out for an additional four days, the union nurses returned to work at 7 a.m. Wednesday.

The two sides have agreed to meet again to resume contract negotiations on Monday.

The hospital went into full ambulance bypass two days before the strike, requesting ambulances not bring any patients to the emergency room and instead take them to other hospitals. The hospital lifted the bypass Wednesday morning, and resumed full trauma services.

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The medical center also transferred several patients to other facilities before the strike, and rescheduled some elective procedures while union nurses were off the job. UCMC also temporarily closed some units of the hospital during the walkout.

Some patients who were transferred to other hospitals will return to UCMC, and the hospital will reopen units that were closed due to the strike.

“Our clinical teams, including our nursing leaders, are focused exclusively on helping the Medical Center rapidly return to full operations after the union walkout,” said Sharon O’Keefe, University of Chicago Medical Center president.

One of the sticking points in contract negotiations has been staffing. National Nurses United said the nurses have filed more than 1,700 complaints detailing staffing problems since January 2017.

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However, the hospital has said staffing is not an issue, arguing their staffing levels are the best in the state and city, and that the number of staffing complaints from nurses represent less than half a percent of all staffing assignments during that time.