The payroll slice, which accounts for 11% of its staff at the location, will go into effect in June.
Impacted workers were given 60-day notices late last week in accordance with federally mandated Worker Adjustment and Retraining Notification Act requirements.
The equipment maker said the decision to cut the jobs at the plant, which specifically produces mining equipment, was needed so production could be brought into balance with demand.
“While some cost reduction measures such as temporary lay-offs, shutdowns and shortened work weeks have already been implemented, more permanent measures must be taken in the near term,” the company said.
“We know this is difficult for our employees and their families but we are taking steps to position the company for long-term success.”
The South Milwaukee cutbacks first announced late last month equate to about 40% of its unionized staff.
According to the Milwaukee Business Journal, Caterpillar started contract negotiations with local United Steelworkers representatives.
The contract for the 800 workers there expired at the end of April.
While a Cat spokesman did not immediately respond to an ILN request for more information on the move Friday afternoon, company spokeswoman Rachel Potts told the Associated Press she could not say whether more lay-offs were on the way in Decatur or any other of its locations.
Decatur had about 4100 employees before the furlough announcement.
Peoria-based Caterpillar also produces construction equipment, diesel engines and locomotives.