Winston Peters is promising to boost the wool industry by forbidding the use of synthetic carpets and insulation in Government-funded buildings if NZ First is part of the next Government.
Prime Minister Bill English says Mr Peters has no idea whether it's a viable scheme and a National-led Government isn't going to start giving guarantees that any particular products will be purchased.
"New Zealand hasn't operated that way for a long time and we're not going to start now," he told reporters.
"It's an unrealistic conversation anyway because Mr Peters has no idea whether it's commercially viable on the Government's terms."
Mr English said the industry might find the Government isn't such a good customer because it wants large volumes at low cost.
Mr Peters is in the South Island on his regional campaign tour and pitched his new policy at wool producers.
"Whether a Government office or a Housing New Zealand property, where carpet is specified it will be natural wool or fibre from here on in," he said on Monday.
"New Zealand First will swing Government procurement in behind natural, renewable and sustainable wool and natural fibres."
He says 20 years ago wool was a $1 billion a year export and it's fallen to $531 million.
"Wool and natural fibres are wonder products and government can help take them to the next level," he said.
The Taxpayers' Union has worked out that the policy would cost $120 million - equivalent to the annual tax take from 6000 average households.
The calculation is based on official estimates of government floor space and the standard price for wool carpets.
"In the lead up to the election, we would encourage all political parties to provide costings with their policy announcements," it said.