The firms are fuming that the bundled 21st century Welsh schools framework went to six english contractors.
They argue the move is anti-competitive and threatens the existence of the Welsh contracting industry.
Councils in Gwynedd, Ceredigion and Powys awarded the work to Bam, Carillion, Laing O’Rourke, Willmott Dixon, Kier and Vinci.
North Wales contracting bosses yesterday met with Welsh Office Minister David Jones to voice their bitter opposition to the actions of the local authorities in the North of Wales.
He met with Chris Wynne, managing director of Denbighshire-based Wynne Construction, and Glyn Watkin-Jones, chairman of Bangor-based Watkin Jones and Nigel Roberts, commercial director at Rhyl-based Roger W Jones, in Llangefni.
Wynne said: “We’re not against frameworks but we want a chance to compete for the work.
He warned: “At the moment they’re working against us. If it carries on it will signal our demise.
The contractors were also joined by Paul Williams, Welsh Conservative Assembly Candidate for Ynys Môn.
After the meeting Williams told the Daily Post: “It’s not just about getting the best price it’s about giving companies like these a fair shake of the stick.”
“If contracts like these go out of North Wales to companies in other areas then those companies often use their own suppliers, not suppliers in this area.”
The Welsh Office Minister underlined the coalition’s commitment to seeing 25% of government contracts going to SMEs.
“We have introduced measures to achieve this and recognise SMEs are the backbone of the Welsh economy,” he said.
“From Whitehall’s perspective, we are keen to see SMEs having a full opportunity to seek government contracts.”