Leaders representing 2,243 Myanmar employees at processing factories owned by Sea Value Group submitted a petition "requesting increased welfare benefits and change of work conditions", the Migrant Worker Rights Network said in a statement.
"The main demands are for increased bonus, increased night shift allowance, increased incentives," Andy Hall, an activist with the network, told AFP, noting the workers had previously won concessions on reducing recruitment fees.
The sector is mainly staffed by poor migrant workers from Myanmar, Laos and Cambodia.
But their treatment has caused increased jitters among international buyers, especially in Europe and the United States where consumers are demanding better ethical sourcing of food.
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According to its website, Sea Value Group's factories process more than 1,000 tonnes of tuna, sardine, mackerel and other fish a day, much of it exported to Europe and the US.
The website says the company's products "meet and exceed consumer expectations with good manufacturing practices, ethical standards and promoted industrial and environmental sustainability".
Thailand's migrant workers have become increasingly vocal in recent years in pressing for better pay and conditions. But doing so can be fraught with risk.
Many employees remain undocumented, despite recent government efforts to register all migrant labourers.
That leaves many migrants vulnerable to abusive employers and traffickers.
Thailand also does not allow migrant workers to form trade unions. Many who do complain find themselves out of work or even prosecuted under defamation laws.
The company denied the allegations and the workers found themselves charged with defamation and arrested for theft of the time cards they used to prove their long work days.
Last September Hall himself was convicted of criminal defamation and given a suspended jail sentence over a report alleging abuses in Thailand's lucrative fruit industry. He has since left the country.
But Thailand's poor labour reputation is starting to catch up with it.
The European Union has threatened to ban all its seafood products unless the military government tackles rampant illegal fishing among its fleets.