(Minneapolis, MN)  —  The deadline for the Minnesota Nurses Association and several Twin Cities and Duluth hospitals to reach a contract agreement is fast approaching.  As many as 15-thousand nurses could go on strike starting next Sunday.  Last week, the nurses union authorized a second strike at Twin Cities, Twin Ports, and Two Harbors hospitals.  Hospital staffing remains a sticking point.  Hospital officials say any work stoppage could lead to closure of some mental health and critical care units.