About 100 employees associated with the line learned of the layoffs Wednesday.
April will mark the end of vehicle production at the Janesville plant that traces its roots to 1919 and the Samson Model M tractor. Chevrolet production started in Janesville in 1923.
The Isuzu line and its employees build about 25 trucks four days a week. The cab-forward truck is commonly used as a delivery vehicle.
GM and Isuzu strengthened their partnership in 1994 with the launch of the NPR gas-powered trucks in Janesville. Two years later, GM and Isuzu started a separate project that put Isuzu-designed cabs on GM's medium-duty chassis. That line eventually moved from Janesville to Flint, Mich.
What remains in Janesville—at least until April 23—is the NPR "W" series. The truck is Isuzu designed and engineered except for its GM power train.
Wednesday's announcement has been expected for months.
GM said last June it would end local production of light-duty trucks—Suburbans, Tahoes and GMC Yukons—by the end of 2010 at the latest. It also said it would shut down the medium-duty Isuzu line sometime in 2009.
SUV production ended in Janesville on Dec. 23, a little more than five months after the plant lost a second shift of production.
More than 2,000 hourly and salaried GM workers were laid off as a result of the production cuts. Supplier companies laid off another 1,200 people.
GM spokesman Chris Lee said Wednesday that a handful of skilled trades employees will remain at the plant after shutdown of the Isuzu line.
Whether 100 employees are ultimately laid off remains to be seen. Earlier this month, GM offered all 62,000 of its hourly employees an attrition program that includes a cash payment of $20,000 and a $25,000 car voucher.
Workers have until March 24 to accept the offer and cut their ties to the automaker.
Lee said it's premature to speculate what will happen to the 4.8 million-square-foot plant that sits on 250 acres on Janesville's south side.
But if the past is any indication, GM has established a pattern for its non-production plants.
GM likely will deploy what it calls a "reuse team" to Janesville to assess everything in the plant. Equipment that can be salvaged for use in other plants will be saved. Equipment GM doesn't want will find its way to auction.
GM also is likely to launch concurrent surveys of the plant's environmental status and any possible reuses for the property. Such studies could take six months to a year.
The environmental assessment will include soil and groundwater testing, and if a cleanup is necessary, GM will develop a plan in conjunction with state and federal environmental agencies.
In the meantime, GM likely will try to market the property. A real estate development company likely will be hired to determine possible uses and values.
A local task force, however, hopes that can all be avoided. The group is lobbying the automaker to award Janesville a different product.
The group met with GM officials last fall but has been held at bay while the automaker tries to sort out its massive financial problems.