One complaint is over the imposition of "zeroing" and the other over "continuous-bond" payments.
Thai Frozen Foods Association president Poj Aramwattanont said separate complaints had better chances of success. It is clear the United States has broken WTO rules, he added.
Thailand has already complained about the US moves, but in a single allegation. It said zeroing and continuous-bond payments were unfair. The complaint was made in March last year.
The association felt that together the complaints were too complicated and this was the reason for such slow progress.
Thailand argued that the US improperly calculated anti-dumping fees by a complicated procedure for determining tariff rates known as "zeroing". It also said the procedures for paying the levies were "overly weighty".
Poj said the separate petitions would shorten the investigation process and could encourage the US to enter negotiations with Thailand.
"Shrimp-exporters are confident of winning the zeroing case as it has already been judged as unfair by the WTO in another case," Poj said.
The WTO found zeroing led to artificial and inflated margins of dumping and thus higher duties, but it sided with the US in a zeroing dispute initiated by Japan, saying most of the examples cited by Tokyo did not violate international rules.
Besides anti-dumping duties, Thai shrimp exporters face a 100-per-cent bank-guarantee payment in the United States known as a continuous bond.
Exporters have still to receive any return from Washington of these payments, imposed in 2005.
According to the association, exporters have paid more than US$100 million (Bt3.46 billion) in bonds as well as anti-dumping duties of between 5.79 per cent and 6.82 per cent of shipment values.
Source: The Nation
Firms to press US complaints
THAILAND - Shrimp exporters will ask the Commerce Ministry this week to file separate complaints against the United States at the World Trade Organisation.