The union representing Allina Health hospital nurses filed a complaint Wednesday — one year to the day after ending a 37-day strike — over the continued assigning of patients to supervisory charge nurses.

Allina leaders haven't lived up to a key provision in the contract that ended the strike, said Emily Sippola, a nurse at United Hospital in St. Paul: a commitment to meet and discuss how to prevent charge nurses from being overworked by being assigned patients.

"It's like flying a plane while also working as an air traffic controller," said Sippola, co-chairwoman of the hospital's nurse bargaining committee.

A written response from Allina called the union's position a misreading of the contract.

"The agreement … was to meet and review situations in which the charge nurse did take a patient assignment and determine whether that was appropriate," the statement said. "We have made substantial progress on these reviews, and they will be completed by the end of the year."

The Minnesota Nurses Association wrote Allina and demanded mediation to address charge nurse staffing. Nurses from Abbott Northwestern in Minneapolis, Mercy in Coon Rapids, Unity in Fridley and United also presented a petition.

Sippola works about half her shifts as a charge nurse. She manages her unit, supports nurses who have complex cases, responds to emergencies and coordinates care with doctors.

Charge nurses often help patients get out of bed on her postoperative cardiac unit, she added, because patients aren't allowed to use their arms in any way that could reopen wounds or disrupt their newly implanted cardiac devices.

"In a crisis, yes, taking direct care of a patient is what a charge nurse would do," Sippola said. "But that's not the expectation of the hospital. Their expectation is that we as charge nurses would do double duty all the time."

An Allina spokesman said the assigning of charge nurses to patients usually occurs at night.

A company analysis found charge nurses were working without patient assignments for 81 percent of nursing shifts at United, and that there was no drop-off in care when charge nurses did take on patient care. Sometimes charge nurses choose to take on patients when a shift is slow, he added.

Allina hospital nurses went on strike twice in 2016 for a combined 44 days. They primarily disputed the health system's demands that they switch to cheaper health insurance but also sought changes in nurse staffing policies.