Flight Instructor with student reported maintenance crews were performing work on the active runway at a non-towered airport and refused to leave the runway; despite multiple aircraft having to perform go-arounds.

Narrative

On Day 0 at XA:30; Aircraft X; a Piper Cherokee 140; was being operated by my student and me (the flight instructor). When practicing touch and go landings at ZZZ airport; a vegetation company was providing maintenance work on the taxiways and runway. When coming in on the final to land for runway XX; the maintenance company was spotted spraying fertilizer on the active runway. One other aircraft was in the traffic pattern for runway XX and was also being forced to go around due to maintenance personnel being on an active runway. The employees of the company would not vacate the active runway when planes were taking off or landing. Once the issue developed; numerous aircraft tried making contact with the company on the runway over the radio CTAF frequency. We were informed by the foreman of the crew; 'Maintenance work is being conducted on this runway'. There were no NOTAMS published on the AWOS frequency or on any FAA-approved websites for the maintenance being conducted on an active runway. This incident caused a threat to the safety of the aircraft in the traffic pattern; and I wanted to make sure it was documented if future occurrences happen.