Heads should roll at KiwiRail after the state-owned company imported wooden sleepers infested with fungi not found in New Zealand, minority party New Zealand First says.
KiwiRail imported 100,000 sleepers which weren't up to hardwood standard and laid 7000 of them, the NZ parliament was told last week.
Transport Minister Gerry Brownlee said the 7000 had "some degree of decay" and were being replaced.
KiwiRail chief executive Jim Quinn said tests showed two of the fungi types on the sleepers were new to New Zealand, TVNZ reported.
They posed no danger to people and the Ministry of Primary Industries (MPI) was investigating whether they posed any bio-security risk, he said.
"However, we are now taking extra steps as recommended by MPI to sanitise and contain the sleepers we are systematically removing from the network."
NZ First Transport spokesman Brendan Horan today said the damage the two new fungi could inflict on the environment could be dramatic.
"Either KiwiRail imported untreated wooden sleepers, or the treatment process was useless.
"KiwiRail management must now do the right thing and make those responsible for this blunder pay with their jobs," he said.
The NZ railway network has six million sleepers.