Ross Gavey of Total Technical Solutions (TTS) said workers could be made redundant because the project was not running as planned.
The company was working with telecom firm JT on the States-backed roll-out, connecting homes to fibre optic cables.
JT said the project was still on target but TTS had "lost out" on a deal with its contractor CH2M Hill.
Mr Gavey said: "TTS sourced local islanders, many of them out of work, for employment in engineering, planning and call centre positions.
"We are proud to have employed previously out of work islanders and supported their training in order to achieve the high level of skill necessary for a project of this scale.
"We have more than fulfilled our contractual obligations and provided a valuable service for the island in getting local people back to work."
Graeme Millar, CEO of JT Global, said it was just a case of contracts changing.
He said JT subcontracted the work to CH2M Hill who then used Total Technical Solutions and that contract had now come to an end.
He said: "The project is on course, it is on track, two of the three major elements are on schedule, one [which involves getting] homes connected, is a bit behind schedule.
"We have looked at mistakes we made in the last year, we have corrected them and our main contractor has started to do things in a different way and I'm sorry TTS have lost out in that."
About 100 staff working on the roll-out of fibre optic broadband in Jersey may lose their jobs, their employer said.