Two taconite mines in the Upper Peninsula of Michigan could shut down at midnight Friday if the plants' owners and the United Steelworkers union don't reach agreements on new contracts.
Three mines in Minnesota's Iron Range also would be effected.
The mines are owned or operated by Cliffs Natural Resources, ArcelorMittal and U.S. Steel.
The negotiations are taking place in Pittsburgh as part of a larger set of nationwide talks between the steel companies and the Steelworkers over contracts that all expire at midnight Friday.
So far, both sides are keeping quiet and refusing to even name the major unresolved issues in the Cliffs and U.S. Steel talks.
But Steelworkers say ArcelorMittal wants deep concessions.
More than 4,000 mine employees in Minnesota and Michigan are among around 29,000 Steelworkers nationwide who are covered by the talks.