By Clare Arthurs BBC correspondent

A spokesman for Vietnamese seafood producers, Nguyen Van Kich, said the petitions asking for steep tariffs on shrimp imports goes against the trend of global trade liberalisation which the US claims to champion.

Shrimp farmed in Asia accounts for much of the US market

Thailand has already promised to back its shrimp industry in the case.

Some shrimp producers in Asia are accusing the US of blatant protectionism.

If the US shrimp producers win the argument that importers are dumping cheap product onto their markets, Washington will slap taxes on imported shrimp, forcing up the price and making it less competitive against locally produced seafood.

Last year Vietnam lost a bitterly fought campaign against a similar move by US catfish producers.

But the shrimp market in the US is worth a lot more. Vietnam sells about $500m worth of shrimp to the American market, compared to less than $60m in catfish.

But this time Hanoi will not be fighting its giant trade partner alone. Thailand and India are also major US suppliers and there is already talk of a coalition.

The legal case also names China, Brazil and Ecuador. The loss of the American market would be a blow to shrimp producers.

Many turned to the American market after Japan and the European Union restricted their import of shrimps from markets including Vietnam, over concerns about the use of antibiotics in seafood production.

A ruling is expected in February.