Is the worker sinful for obeying the contractor who violates the terms of the contract and requests a reduction in some rebar and reinforced concrete?

A contractor's violation of contract terms without the knowledge or consent of the responsible authority is forbidden deception. A worker's commission of such a violation is forbidden obedience, which necessitates punishment. The sin is further compounded if it results in endangering people's lives and property. The worker must cease the work if he cannot refrain from this (forbidden) obedience and must inform the competent authorities. He must trust that whoever fears Allah, Allah will make for him a way out and provide for him from where he does not expect.