One of three big contractors installing fibre cables for telecommunications giant Chorus has pulled the pin.
Construction company Downer will no longer carry out the work, reportedly because it's not profitable.
E Tu Union spokesman Joe Gallagher says Chorus has been underpaying for some time, and now the entire ultra-fast broadband project is at risk of falling over.
"It's a serious sign when a high-quality contractor like Downer signals intention to move away from this business. You have to ask why."
He fears the gap Downer leaves will be replaced by cheap foreign workers brought in on temporary work visas.
"The fact that Chorus continues to promote and support this low-value contracting model is disgraceful."