Gangmasters should be licensed to prevent a repeat of the deaths of the Morecambe Bay cockle-pickers, ministers are being told.
Hundreds of livelihoods depend on cockle-picking
The call came after it emerged that some overseas workers recruited to pack food for UK supermarkets are being left with wages of just 78p a week.
Labour MP Jim Sheridan says his Bill to licence gangmasters has attracted widespread support.
But "there was some way to go" before ministers gave their complete backing.
Twenty migrant workers drowned on 5 February when they were caught in the dark on the mudflats at Morecambe Bay by a rising tide.
A team of Chinese police officers is being sent to the UK to help identify the cockle-pickers' bodies.
Don Pollard, a Transport and General Workers' Union official, told reporters in London that he had interviewed seven South African workers on Tuesday who he believed were being exploited.
After recruitment in South Africa, they were lent money which they had to repay at 100% interest, were living in cramped conditions and were being paid below the minimum wage, he said.
Some 24 workers were living in one house, paying £55 a week for accommodation and £17.50 for transport and administration.
Mr Pollard said one of the workers showed him his pay packet which contained 78p after all other expenses had been removed.
The workers were packing fruit for sale in supermarkets and Mr Pollard claimed they were being paid just £4 an hour.
Mr Sheridan said the case showed the need for his Bill which is due for a second reading in the Commons on Friday.
"As the people of Britain now know following Morecambe Bay, allowing the unscrupulous to thrive and the failure to protect workers can have the most tragic human consequences," he said.
"The government has said it back the principles of my Bill and I hope they will now help me to progress this important legislation."
Jack Dromey, Transport and General Workers' Union deputy general secretary, said: "The weaknesses of the law are undermining reputable labour providers and responsible retailers and allowing the ruthless exploitation of vulnerable workers, many of whom are working legally.
"This Bill would ensure that gangmasters must obtain a licence and operate transparently, establishing the paper trail that has been missing which has helped illegal employers operate beyond the law."