In an escalation of the tension in the ongoing negotiations between the United Auto Workers and General Motors, UAW members went on strike at 11 a.m. ET today.

Approximately 73,000 UAW workers began walking off the job and taking up their pickett signs outside GM facilities.

Talks between the largest automaker in the United States and the union are on-going but the original contract between the two entities expired nine days ago on September 14.

The strike action will effect 59 General Motors facilities and production plants in the United States although 100,000 UAW workers remain on the job with Ford and Chrysler.

The union extended its contracts with both Ford and Chrysler, using the General Motors negotiations as a forum to forge a new contract that will, in turn, serve as a model for agreements with the other automakers.

A major stumbling block in the talks is the issue of shifting the responsibility for some $51 billion in future health care expenses from the automakers to trust funds controlled by the unions.

Approximately 340,000 retired GM workers or their spouses currently receive benefits from the automaker.

The company maintains that in order to remain competitive with foreign companies it must close the gap in operating and benefit costs.

Although no current statement has been forthcoming from the union, Sunday the UAW indicated the the company had not adequately addressed union concerns on job security and other major points of contention.