The Labour Party says if it wins the election in November it might reverse the ultra-fast broadband contracts without compensation.
Legislation which will put in place the framework for the Government's ultra-fast broadband policies is making its way through Parliament.
Telecom won the right to build the fibre optic network in Auckland, the eastern and lower North Island and most of the South Island.
The total cost of the scheme is about $3.5 billion.
Labour says the legislation underpinning the contracts sets up a monopoly that puts investors ahead of consumers.
Senior MP Trevor Mallard says it wants to make it clear that anyone entering into an arrangement based on the legislation has to know that it may not last should Labour become government.
ACT Party leader Don Brash says the position is economic thuggery and Labour has not stopped to consider the effect its position might have on investor confidence and New Zealand's fragile economic recovery.