Some foreign workers are exploited in the agriculture sector
A helpline to report the mistreatment of workers and illegal pay rates is being launched by the government to clamp down on rogue employers.
A new board will coordinate the work of the groups which check that firms kept to the rules on treatment of staff.
Unions welcomed the move but said an opportunity to expand the Gangmasters' Licensing Authority had been missed.
They had wanted its remit to be extended to care workers, and the construction and hospitality sectors.
An information campaign will be launched later to raise awareness of employment rights and how to enforce them.
And a new Fair Employment Enforcement Board, including trade union and business figures, will oversee the work of enforcement groups checking minimum wage payments, health and safety, employment agencies and gangmasters.
Employment relations minister Pat McFadden said: "Compared to a decade ago there are three million more people in work in Britain and they all enjoy more employment rights than they would have in the past.
"Important minimum standards on wages, paid leave, maternity leave and conditions have been put in place.
"However, there are still dark corners of the labour market where rogue employers seek to mistreat their workers and more needs to be done to safeguard people's rights."
Under the Gangmasters Licensing Act, everyone who supplies workers to the agricultural and food-processing industries must hold a licence.
It was set up in 2005 to protect low-paid workers and oversees treatment of about 500,000 workers.
TUC general secretary Brendan Barber said the government should have taken the chance to widen the scope of the act to new sectors.
And the UCATT construction union said it was baffled by the decision not to extend its remit, saying there is endemic abuse of vulnerable workers in the building industry.
A government spokesman said the committee advising ministers could not agree about extending the role of the act.
Meanwhile, the Recruitment and Employment Confederation says that existing regulations ensure that workers in these sectors are protected.
Tom Hadley, of the trade body, which supports and represents the recruitment industry, said: "These are very different labour markets and just to impose the same system there isn't guaranteed to work.
"One of the counter arguments to licensing is that it's actually quite expensive, so I think the focus at the moment has to be on enforcing the regulations already out there by having more inspectors."
Richard Dunstan, of Citizens Advice, said the single telephone number to report rogue employers would be of "immense benefit".
"A great many of the clients we see with employment issues are vulnerable workers, who are too afraid of losing their job to report abuses," he said.