Exporters are struggling to get shipping space due to reduced vessel capacity and the seasonal peak in production.
Export New Zealand executive director Catherine Beard said container space was a major issue, especially at Port Otago, Port of Lyttelton and Port of Napier.
It affected exporters of low-value commodities the hardest, she said.
Major exporters tended to have contracts with shipping lines which gave them greater surety, but Ms Beard said she has been told some of those companies were also experiencing problems.
"I think it's a problem every year when seasonal products come on the market, but it is worse this year because of the contraction of shipping services," she said.
There were reports from Port Otago that customers with lower-value goods were being bumped - or losing pre-booked space - but that the issue was no worse than other years, Ms Beard said.
Most exporters using Port Otago had contracts with shipping lines.
A spokesman for Port Otago could not be reached for comment.
In other years, exporters who were bumped off a vessel would not have to wait long, but this year, Ms Beard said, they faced a wait of four to six weeks before getting shipping space.
While the problem was in part due to the export season peaking, shipping lines had rationalised to address an oversupply of space.
Ms Beard said companies were also sailing their ships at slower speeds to keep costs down.
"This slow steaming results in longer delivery times for exporters, has shelf life implications and could require greater inventory levels."
She suggested exporters of lower value goods could team up with exporters of high-value products to share space.
