The US has said it will halt imports of five types of farmed Chinese seafood, claiming they contain antibiotics that are not allowed in North America.
Chinese exports have surged as their prices have stayed low
The Food and Drug Administration (FDA) said it would detain shipments of catfish, basa, shrimp, dace and eel.
But the FDA said it was not recalling seafood already in the US, and that drug levels were not dangerous and only slightly above detectable levels.
This is the latest in a number of US warnings about Chinese products.
In past weeks there have been concerns about contaminated toothpaste, dog food and the paint used in toy trains.
China countered that its exports were no threat to health and "guaranteed" the safety of its products.
The FDA said it had found that Chinese seafood tested between October 2006 and May 2007 was repeatedly contaminated with antimicrobial agents.
Some of the substances included nitrofuran, malachite green and fluoroquinolone, which, according to the FDA, may help build up a resistance to antibiotics when used in food animals.
"We're taking this strong step because of current and continuing evidence that certain Chinese aquaculture products imported into the US contain illegal substances that are not permitted in seafood sold in the US," the FDA said.
"We will accept entries of these products from Chinese firms that demonstrate compliance with our requirements and safety standards," it added.
Chinese exports to the US and other Western nations have boomed in recent years.
In May, China's trade surplus hit $22.4bn (£11.4bn), up 73% on the same period last year. The full-year surplus is on track to hit a record in 2007.
While that is good news for Chinese exporters, it has increased pressure on foreign governments to protect their domestic producers, and increased complaints that China is flooding markets with impossibly cheap goods.