Salvors working on the Rena say pirates stole some equipment en route to New Zealand, that would have been used in the operation to reduce the ship's bow.
The ship struck the Astrolabe reef off the Tauranga coast a year ago on Friday.
An American company, Resolve, is reducing the Rena's bow section to below the water line, by cutting it and removing it piece by piece.
Resolve salvage master Frank Leckey says a crane barge that will be involved in the salvage operation was en route from Singapore when it was raided by pirates.
Unique equipment needed for the divers was stolen.
Mr Leckey says the raid is more of a financial blow than a setback.