The Minnesota Nurses Association said Monday that nurses' complaints about unsafe hospital practices have increased sharply over the last three years, with the chief concern being delayed or incomplete care of patients due to inadequate staffing.

Whether the increase reflects growing safety problems in Minnesota hospitals, or just more reporting of existing nurse concerns, is unclear, but the study authors said the results demand attention. Complaints alleging delayed treatment rose from 1,362 in 2014 to 2,131 last year, while complaints of hospital units being significantly understaffed for safe patient care increased from 136 to 436.

"When you're understaffed by that amount, nurses aren't able to just 'do the best that they can' and 'make ends meet'‚ÄČ" for all of their patients, said Mat Keller, a regulatory specialist for the union and co-author of the report.

A spokeswoman with the Minnesota Hospital Association said the report is a "political stunt" and that nurses are required to report actual safety concerns to their supervisors and state regulators.

"People should not view it as something that is complete or a trend, or real because these are filled out by union members at union hospitals only, and they urge their members to fill them out," said Wendy Burt, an association spokesperson.

The union has encouraged nurses to file unsafe staffing reports since the early 1990s, and the incidents often become hot topics during nurse contract negotiations and legislative debates over nurse staffing. The complaints have no regulatory teeth, though union officials have sometimes brought the more severe allegations to the attention of hospital licensing investigators at the Minnesota Department of Health.

The study represents the second annual attempt by the union to quantify the nurse complaints and look for trends. Not all news was bad; complaints about unsafe staffing practices leading to patient falls declined from 357 in 2014 to 224 last year.

The report also tallies how hospitals respond to staffing concerns; 488 of the complaints involved situations when the hospitals had to close units due to a lack of nursing staff. And in 187 instances last year, nurses filed complaints indicating that they refused to take on new patients because they felt it would jeopardize their ability to safely monitor all of their patients.

Exactly how last year's strike by more than 4,000 Allina Health nurses affected complaint reporting is unclear. Keller said the increase in complaints in 2016 is surprising, considering that so many Allina nurses were off the job for weeks in June, September and October.

Burt said the report is motivated by a long-running union demand for fixed ratios of nurses to patients, which could inflate health care costs. They want a "government mandated number of nurses," she said, "on every unit on every hospital at all times."