The EU has given Thailand, the world’s third-largest seafood exporter, six months to crack down on illegal fishing or face a trade ban on its fish imports.

South Korea and the Philippines though have escaped the commission’s net after bringing in legal reforms and improved control and inspection systems.

“The commission has put Thailand on formal notice, after identifying serious shortcoming in its fish monitoring, control and sanctioning systems,” the environment and fisheries commissioner, Karmenu Vella told a press conference in Brussels. “There are no controls whatsoever and no efforts being made whatsoever and illegal fishing is almost totally allowed.”

Unless Thailand now cleans up its fishing industry, it risks an embargo on its fish exports in October. EU vessels could also be prevented from fishing in Thai waters.

To avert sanctions, “as a minimum we would expect that control and monitoring measures and enforcements should come into place,” Vella told the Guardian.

Thailand’s agriculture ministry has announced a six-point plan for combatting illegal fishing. But meeting the EU benchmarks by October is considered unlikely, as Thailand’s legal and regulatory framework for fishing has not been changed since it was drawn up in 1947.

A high percentage of the Thai fishing fleet is unregistered and outside government control. Even registered vessels often sail without strong catch documentation and operation certificates.

“They have a long way to go,” an EU source told the Guardian. “But we are not looking for trade sanctions so it is really up to them to decide.”

The EU’s ‘yellow card’ to Thailand is the most high profile action taken against illegal unreported and unregulated (IUU) fishing, under a 2010 regulation against such practises.

“Yellow-carding has been proved to be a strong incentive for states to combat illegal fishing,” said Tony Long, director of The Pew Charitable Trusts’ Ending Illegal Fishing project. “Commissioner Vella has shown global leadership in implementing the EU’s tough illegal fishing regulation against such a significant fishing state.”

Thailand’s global fish exports were valued at €7bn (£5bn) in 2013. Last year, €642m of that catch – weighing 145,907 tonnes – was destined for European dishes, where it made up over 3% of the continent’s overall fish imports.

According to Eurostat, the UK has the largest appetite for Thai fish, consuming over €153.4m of it a year, closely followed by Italy, Germany, France and the Netherlands. Much of that will have been caught by pirates.

Illegal fishing in the Asia-Pacific region killed between 3.8-8.1m tonnes of fish in 2014, according to one report. In Thailand, up to 39% of wild-caught seafood entering the US market last year is estimated to have been unlawfully caught.

Illegal fishing trawlers have also been accused of using Thais as slave labour on fishing expeditions, with their catches entering the global food supply chain via Thai ports.

After the de-listing of South Korea, the Philippines and Belize, Cambodia, Guinea and Sri Lanka are the only countries affected by the ‘red card’ from Brussels for illegal fishing. While welcoming news that Thailand could soon be joining it, some conservationists protested that the de-listing had been premature and partial.

“Serious concerns remain about the South Korean fishing fleet and the role of the Korean authorities in clamping down on illegal fishing,” said the Swedish Green Party’s fisheries spokesperson, Linnéa Engström. “South Korea has introduced new legislation but this has been criticised as insufficient and cosmetic, while implementation remains open to question.”

The Greens argue that European trading interests with Korea have been allowed to trump marine conservation, even as the threat of EU sanctions has led other countries to revise their fishing laws.

Fish catches measured per unit of effort in the Gulf of Thailand and Andaman Sea have already plunged by more than 86% since 1966 and boats now catch just 14% of what they caught in the mid-1960s, according to the Environment Justice Foundation.

Depleted fish stocks have spurred a ‘ghost fleet’ of unregistered pirate ships that plunder the waters of other countries, often under assumed identities, the group says.

An estimated 11-26m tonnes – or 15% - of the world’s fish are caught illegally each year.