CHICAGO (CBS) — Classes have been canceled for roughly 2,500 students in the northwest suburbs, after teachers in McHenry Community High School District 156 went on strike overnight.

Contract talks with the district broke down just after 1 a.m. Thursday, following about six hours of last-ditch negotiations.

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Approximately 160 teachers and support staff began picketing around 6:45 a.m. outside McHenry East and McHenry West high schools.

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Heidie Dunn, spokeswoman for the McHenry Community High School Educators’ Association, said it’s the first teachers strike for District 156 since 1985.

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The two sides have been negotiating since March, and began Wednesday’s session far apart on two major issues — pay and insurance benefits.