(CBS) — Last-ditch contract negotiations resumed at 7:30 p.m. Wednesday between the McHenry High School District 156 administration and teachers who are threatening to strike Thursday morning if no contract agreement can be reached.

The two sides began the session far apart on two major issues — pay and insurance benefits. McHenry Community High School Education Association spokesperson Heidie Dunn said students and teachers were on edge Wednesday at McHenry East, where she teaches honors English.

District 156 teachers have struck once, in 1985, but Dunn said they came close two years ago. The District has posted an advisory on its Web site saying that there will be no classes, extra-curriculars or sports should a walkout occur.