Subcontractors rolling out the National Broadband Network (NBN) are being subject to "classic bully boy tactics", the federal opposition claims.
Up to seven subcontracting companies in South Australia have reportedly walked away from the roll-out, saying NBN Co's construction partner Syntheo has refused to hand over hundreds of thousands of dollars in unpaid fees.
The subcontractors were also made to sign strict gag orders stopping them speaking publicly about the work carried out, The Australian reports.
Opposition communications spokesman Malcolm Turnbull said the confidentiality clauses were designed to stop people telling the truth about the project's mismanagement.
"Because if they do so, when they do so, it causes political embarrassment to the Labor Party," he told AAP.
"What they're trying to do is to shut these people up and it's a classic case of bully boy tactics."
Mr Turnbull said both contractors and subcontractors were being "screwed" as the NBN tries to meet unrealistic construction costs.
"Contractors are losing a fortune, subbies are losing a fortune," he said.
"It's actually sending, in the case of the subbies in particular, businesses to the wolves."
NBN contractor Syntheo will pull out of work on the network early next year, after finishing work on existing contracts in Western Australia and South Australia.
Mr Turnbull reiterated that a coalition government would audit the entire project, including the company's board, if elected to government.
Labor insists the rollout of the NBN in Western Australia and South Australia will still happen on time and on budget.
