A failure to hold companies to account for lesser labour abuses from late wage payments to excessive overtime creates a breeding ground for the worst forms of modern slavery to thrive, the top United Nations expert on human trafficking said.

Businesses are judged only on their efforts to curb extreme forms of labour exploitation, leaving more common abuses unchecked and likely to lead to even poorer working conditions, according to U.N. special rapporteur Maria Grazia Giammarinaro.

Minor labour abuses are so widespread that workers often do not realise they are being exploited, or are reluctant to speak out for fear of backlash – from being fired to deported in the case of undocumented migrants – the Italian judge said.