An estimated 3,000 gangmasters working in the UK food and farming industries must now apply for a licence to operate.
The scheme, introduced under the new Gangmasters Licensing Act (2004) to stop exploitation of illegal workers, covers agriculture and horticulture, shellfish gathering, processing and packaging.
The act will also protect workers on issues such as minimum wage and health and safety and creates a new body, the Gangmasters Licensing Agency (GLA), to support legitimate operators.
Jim Sheridan, MP for West Renfrewshire, who campaigned for legislation, said: "I look forward to the GLA getting down to the business of supporting legitimate operators and driving the criminals out."
The Department for the Environment, Food and Rural Affairs was due to have established the Gangmasters Licensing Authority to police the act by this month.
Problems with illegal workers continue to dog the industry. A group of 11 were arrested at Kettleby Foods in June after the firm found discrepancies in work documents.