A belated Thai clampdown on illegal fishing is forcing unlicensed vessels ashore, threatening to paralyse the key industry as the kingdom desperately tries to avoid a European Union ban on exports worth $1 billion a year.

Barrels of fish packed in ice are rolled off boats at a bustling port in Samut Sakhon, a coastal province near Bangkok, by the Myanmar and Cambodia migrant workers who prop up the world's third largest seafood producer.

But many will sit idle from Wednesday, say their Thai employers, who have failed to obtain necessary fishing permits under a raft of new government rules aimed at cleaning up the shadowy industry.

Next to buckets of red snapper destined to become fish balls for the local market and fishmeal to rear shrimp marked for Europe, a Thai vessel owner says there are "too many rules and too little time".

"We will have to keep paying bills with no income," said the worried 59-year-old, who withheld his name, as he prepares to cease operations until he can meet the conditions for a new permit.

The Wednesday deadline to register boats with authorities and acquire permits under revised standards, including installing equipment such as tracking devices, comes after the European Union threatened to ban fish imports from the kingdom unless it combats illegal fishing.

In April Brussels issued Thailand with a "yellow card" for inadequate fisheries monitoring, controls and punishment, warning that a "red card" and eventual import ban would follow if it failed to improve within six months.

The spectre of losing $1 billion in European sales is a shortfall the ruling military can ill-afford in an already sluggish economy.

Thailand saw only 0.3 percent growth in the first quarter and exports have been slowing in part, says the World Bank, due to an erosion in competitiveness.

- EU ban, US ranking fears -

Aphisit Techanitisawad, president of The Thai Overseas Fisheries Association, estimates around 3,000 fishing vessels will renege the seas from Wednesday.

"About 80 percent of all the fishermen, they're coming back to shore" to seek permits, he told AFP at his fisheries factory in Samut Sakhon.

A recent shortage in fresh fish has already seen his workers stop processing crab sticks for French exports, instead focussing on canning sardines and mackerel from frozen supplies for the Myanmar and Cambodian markets.

Aphisit thinks the government could have imposed a more lenient timeframe for changes, but premier Prayut Chan-O-Cha Tuesday told reporters the industry had been unchecked for too long.

Thailand's image has been battered in recent years by a series of fishing abuse allegations from prominent rights groups of ships using slave and child labour as well as trafficking victims.

And last year the US downgraded the kingdom to its lowest ranking on human trafficking, a designation that can trigger sanctions.

Bangkok is desperate to improve its standing, while sanctions have not yet been imposed, laying out new measures including a ban on fishing workers under 18 in the months since. The latest Trafficking in Persons (TIP) report is due for imminent publication.

Observers say that while the latest threat of an EU ban has triggered a renewed sense of urgency in authorities, rushed actions will fail to combat illegal fishing in the long-term.

Improving "monitoring, control and surveillance" will help to tackle longstanding problems of pirate fishing, slavery and trafficking in Thailand's fisheries industry, said Daniel Murphy, a Bangkok-based campaigner for the Environmental Justice Foundation.

But by rapidly regulating the neglected sector the government "risks regularising more vessels than Thailand's exhausted waters can support as well a significant number of vessels which have spent years openly flouting fishing laws", he said.