Between $10 million and $15 million of additional product, which also did not have 1080 testing certificates, would arrive in China over the "next week or so", he said.
"There's question marks as to what sort of certification that product is going to require to efficiently move through the port."
The association has criticised the Ministry for Primary Industries (MPI) for not informing exporters earlier about the new testing requirement.
"We still haven't had any official information," Barnett said.
Watch: 'If you're concerned ring 111'
MPI deputy director-general Scott Gallacher said the ministry was informed of the new certification only this week and it was still working with its Chinese counterparts to obtain further details of the scope of the testing requirements.
"Relevant parties, including the New Zealand Infant Formula Exporters Association, were notified shortly after we became aware of the rationale of what was being requested," Gallacher said.
He said MPI's Chinese counterparts had indicated they were unaware of any products being held up in China as a result of the 1080 threat.
"We do know exports can be held up for a variety of reasons and requirements and clearance times can vary between countries, but also between ports in the same country," Gallacher said. "The normal clearance process for infant formula into China can be up to 40 days."
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The Herald spoke to the infant formula exporter whose product was stuck in Shanghai. He didn't want his company named for fear of the impact it could have on his business, but was adamant his product was held up because of the 1080 test.
Meanwhile, a Fonterra spokesman said the dairy giant didn't have any product held up at the Chinese border, and the 1080 threat had had no impact on sales this week.
Barnett said it appeared Fonterra had managed to get its certification in order before product left New Zealand. "It's not the same case for the smaller exporter."