When police, acting on a tip from a runaway worker, raided a landowner's farm in Sindh province, they discovered more than 140 labourers, many of them women and children, who were chained while they worked in sugarcane fields. Armed guards watched over them.
Pakistani law prohibits forced and unpaid labour, but many of the freed labourers claimed they had been working for their feudal boss, Abdul Rehman Marri, for more than 25 years, trying to pay off their debts.
The amount of money they had borrowed was tiny, barely enough to buy medicine for a sick child, or pay for a daughter's dowry. But the landlord charged them interest on the loan, so that it grew into a staggering sum that the peasants could never pay off. If a labourer died of over- work, his son had to work off the debt.
Anti-slavery activists found temporary shelter for some freed labourers in Christian churches. But according to Aziz Siddiqi, a director of the Human Rights Commission in Lahore, others may have "drifted into the hands of other feudal landlords in Sindh province".
Mr Siddiqi said: "We're concerned about them. They don't have much of a choice, either to starve in freedom, or to end up again in bondage."
In feudal Sindh, the home province of the Prime Minister, Benazir Bhutto, Mr Siddiqi says that "there is a pact among the big landowners to co-operate against the workers".
Human rights activists fear that the families who were freed from servitude may be hauled back to the landlord, Mr Marri, who was not arrested.
"Some of these landowners keep families like slaves. They imprison them at night in stockades with high walls and shackle them. Even when the bonded labourers are working in the fields, they are sometimes forced to wear 25kg fetters on their legs," Mr Siddiqi said.
Few landlords are ever arrested, as Sindh's provincial assembly is controlled by feudal landowners. It was only after a peasant fled from Mr Marri's farm and notified the Human Rights Commission in Sindh that police carried out a raid.
The runaway guided them to the farm where the other bonded labourers had been chained up to stop them from escaping.
Human rights workers were forced to flee after the landowner's gunmen fired shots. But the activists returned with police officers and freed the labourers. "Some were children. They were born into slavery and traded back and forth between the landlords," Mr Siddiqi said.