Some exporters are struggling to send goods overseas because of a backlog of containers at several ports, Export New Zealand says.
Export New Zealand executive director Catherine Beard says securing container space is proving difficult in some cases, particularly on ships leaving the ports of Napier, Lyttelton and Otago.
Shipping capacity is traditionally tight at this time of year, but the problem is being exacerbated by fewer ships due to cutbacks made during the downturn.
Some goods are being delayed by up to six weeks, she says.
The New Zealand Council of Wool Exporters represents companies handling about 80% of the country's wool.
Its president, John Henderson, says council members could, in previous years, get space on a ship within a week but at the moment it is taking a month to six weeks.
The situation is worse than for many years, he says, and if it continues, producers' cash flow will be severely affected.
Mr Henderson says the market for wool has improved in the last few months, and clients have been reasonably understanding, but contracts may be affected if delays continue.
Port of Lyttelton chief executive Peter Davie says shipping lines have cut back on services due to recession, so many of the vessels calling at the port are already full.
Exporters who have longer term contracts are less affected, he says.
The managing director of shipping line Maersk, Julian Bevis, says his company and other lines have increased their tonnage for the peak season, but only to the extent that the vessels can be filled with sufficiently profitable cargo.
Mr Bevis says 2009 was a very tough year, and the industry has to learn lessons from it.