Rules outlawing unlicensed gangmasters which come into force over the weekend will help save the lives of exploited workers, a trade union has claimed.
Morecambe Bay is a popular location for cockle-picking
Under the Gangmasters Licensing Act, unlicensed operators who supply workers to the agricultural and food-processing industries face up to 10 years in jail.
The T&G Union said the Act would help prevent a repeat of a 2004 tragedy when 21 illegal Chinese cocklers died.
The deaths, in Morecambe Bay, Lancashire, prompted the new laws.
The cockle-pickers, all illegal immigrants, were swept away by the tide. Their gangmaster was held responsible and convicted of manlaughter.
The new laws, which come into force on Sunday, affect recruitment agencies as well as gangmasters.
Jack Dromey, of the T&G, said Sunday would mark "the beginning of the end of rogue gangmasters".
He accused them of practising "modern-day slavery", saying "some will go to jail, sending a message - never again, Morecambe Bay".
Official labour suppliers must register with the Gangmaster Licensing Authority (GLA), which said about 1,000 operators out of an estimated 2,000 had so far applied.
Although the rule change comes into force on Sunday, labour suppliers in the shellfish industry have until next April to comply.
And the rules do not cover other industries, such as construction or hospitality - sparking fears that illegal gangmasters could simply move into other industries.
A spokeswoman for the environment department (Defra) explained that the GLA was part of Defra, and so was only concerned agriculture and food.
"Other government departments will look at the GLA and see how it works. If it is successful, then they could bring in similar regulations in other industries," she said.
GLA chairman Paul Whitehouse told the BBC the authority was "doing reasonably well" and had issued 600 licences so far.
But he expressed concern at the numbers of gangmasters who had not applied.
While some of these were simply unaware of the new rules, he said he suspected that others would continue to work illegally.
He pledged to track down illegal operators, saying the public and industry could help by passing on information.
"Those who are in the business and are being undercut by those who are illegal will no doubt be telling us.
"At the same time, we also have our own compliance enforcement officers out there who are getting to know the users of labour."
From 1 December it will also become an offence for a business to use the services of an unlicensed gangmaster or agency.