Who: 12,000 nurses represented by the Minnesota Nurses Association at 14 Twin Cities hospitals.

When: Their contract expires at midnight on May 31, but the nurses must give the hospitals 10 days' notice before striking.

Affected hospitals: Abbott Northwestern, Mercy, Unity, United and Phillips Eye Institute (all owned by Allina Hospitals and Clinics); St. John's, St. Joseph's and Bethesda (owned by HealthEast Care System); North Memorial; Children's Hospitals and Clinics of Minnesota; Park Nicollet Methodist; Fairview Southdale and the Riverside campus of University of Minnesota Medical Center, Fairview.

Issues: Nurses have asked for 3 percent pay increases in each of three years. Hospitals have proposed annual raises of 0, 1 and 2 percent, plus cuts in pension contributions and more flexibility in scheduling nurses.