The Fair Trade Centre and Råd och Rön magazine say that only three out of seven companies that import tinned tuna fish from Thailand enforce an ethical code on their suppliers.
Workers at the factories are paid low wages, work long hours, are forced to work overtime and are discriminated against, campaigners say.
The researchers interviewed workers at three out of the eight Thai factories that supply most of the tuna sold by Abba, Axfood, B&S Foods, Coop, ICA, Lantmännen and Piwa.
Workers at the factories said they were paid below the minimum wage, that guest workers from Burma were discriminated against, that they were made to work overtime and that they worked ten hours a day, six days a week.
Only Axfood, Coop and ICA have codes of conduct covering wages, working hours and UN working rights conventions.
“It’s surprising that four out of seven companies don’t have codes at all. Working conditions in this part of the world have been debated for 10-15 years, said Henrik Lindholm, project leader at Fair Trade Centre.
Lindholm added that of the three companies, only Axfood and ICA follow up implementation of their codes.
“Coop says it is going to start now,” he said.