Nearly 25 workers, including children, who worked 15 hour days for seven years, were rescued at the weekend at Baran in the western Indian state of Rajasthan, in a rare crackdown on farms where forced labour is rampant.
Campaigners said the workers were from a tribe in the central Indian state of Madhya Pradesh and were given loans ranging from 500 to 20,000 rupees ($8 to $308) before being taken to Rajasthan to work in the fields.
"These people were trafficked from their home state with the lure of good work but kept bonded on the fields. They believed they were repaying the loans," said Nirmal Gorana, convener of the National Campaign Committee for Eradication of Bonded Labour, that took part in the rescue.
Rescued workers said while they worked in the fields, their children worked at the employer's house for no money.
"The employers did not give them wages, but only packets of wheat. This too was to ensure they stayed alive to continue working on their fields," Gorana told the Thomson Reuters Foundation.
There are no national figures on the number of people in slavery in India, but the Ministry of Labour and Employment recently announced plans to identify, rescue and help over 18 million bonded labourers by 2030.
In India, villagers are often lured by traffickers with the promise of a good job and an advance payment, only to find themselves forced to toil in fields or brick kilns, enslaved in brothels or confined as maids to pay off debt.
Others work at the bottom of complex supply chains making jewellery, cosmetics, and garments.
Most of the workers rescued at Baran have been sent home, said Gopal Lal, the sub-divisional magistrate at Baran.
He said 18 of them were given release certificates that entitled bonded workers to 300,000 Indian rupees ($4,600)compensation in their home state.
"We have also launched a survey to look for more workers," said Lal.
Campaigners said most bonded labour in India is on the country's farmlands but is often perceived as regular employment and government action is rare.
"Bonded labour on farmlands is not seen as a crime or a problem that can be reported. It is so rampant that it has got societal acceptance," said Bharath Bhushan from the Centre for Action Research and People's Development, a charity that works with the rural poor.