Workers at the Navistar International's IC Bus plant in Tulsa are now members of the United Auto Workers.
In a news release, the UAW says the workers agree to join the union following an election held at the plant earlier this month.
The union says about 650 workers are employed at the facility at Tulsa International Airport.
"We are pleased to have these workers in the UAW," said UAW Vice President General Holiefield, "and we value our healthy and productive relationship with Navistar."
"Joining with other UAW members working at Navistar and other bus and truck companies only makes sense," said UAW Region 5 Director Gary Jones.
Navistar International Corporation is the nation's largest integrated manufacturer of school buses.
The company is based in Illinois also produces commercial buses, commercial and military trucks, diesel engines and recreational vehicles.
The union says Tulsa bus workers join 2,600 other UAW members at Navistar facilities in Indianapolis, Indiana, Springfield, Ohio, Melrose Park, Illinois, Atlanta, Georgia, Dallas, Texas, Conway, Arkansas, and York, Pennsylvania.