Custom Coaches will close its Royal Park site in eight weeks, leaving most of its 75 workers without a job.
The ABC reports that Custom was a year into a five-year contract to supply buses to the SA departments of transport and education.
"We're informed by the administrators that they will still provide those vehicles but that they may be subcontracting to do that," SA manufacturing minister Susan Close told the ABC.
"We will work through whether that's able to occur through any local businesses or whether we are going to have to rely on interstate ones, that's naturally not the desirable position."
Custom was put in voluntary administration on May 30, with Deloitte appointed as administrators.
The administrators broke the bad news to the workers on the same day.
Custom Coaches is owned by British company Alexander Dennis, which acquired Custom in June 2012, with a stated goal of “turn[ing] a successful brand into a GREAT Australian business.”
Custom has manufacturing and maintenance facilities in four states, and makes bodies for Scania.