The EU on Tuesday warned Thailand, the third largest seafood producer, that it had six months to halt illegal fishing or face an import ban in the world's single biggest market.

"Today's action constitutes a warning ... the burden is now on Thailand to take corrective measures," EU Agriculture and Fishery Commissioner Karmenu Vella said.

After discussions on remedies dating back to 2011, the European Commission had decided to issue Thailand a 'yellow card,' with a 'red card' and punishment to follow if there was no improvement, Vella told a press briefing.

"I urge Thailand to join the European Union in the fight for sustainable fisheries. Failure to take strong action against illegal fishing will carry consequences," he said.

The Commission, the EU's executive arm, said Thailand's fisheries monitoring as well as its control and sanctioning systems were inadequate and had to be brought up to international standards.

Belize, Guinea, Cambodia and Sri Lanka were all hit with import bans in the past but remedial efforts by Belize meant it had now been taken off the blacklist, it said.

Additionally, 'yellow cards' against South Korea and the Philippines had been withdrawn after "they carried out appropriate reforms of their legal systems and are now equipped to tackle illegal fishing."

"Both South Korea and the Philippines have taken responsible action, amended their legal systems and switched to a proactive approach against illegal fishing," Vella said.

The Commission said illegal fishing accounted for at least 15 percent of the global catch and was worth up to 19 billion euros a year.

"As the world's biggest fish importer, the EU does not wish to be complicit and accept such products into its market," it said.