Uniqlo owner Fast Retailing Co Ltd said on Thursday it has instructed two suppliers in China to improve factory working conditions after an inspection by the Japanese apparel retailer found several problems including long working hours.

The move came after Students and Scholars Against Corporate Misbehaviour (SACOM), a Hong Kong-based advocacy group, issued a report saying that employees at Dongguan Tomwell Garment Co and Pacific (Panyu) Textiles were working excessive hours in unsafe conditions, including extremely high temperatures, poor ventilation and floors covered with sewage.

Factory safety at suppliers to global clothing brands has been under scrutiny after the collapse of a factory in Bangladesh in 2013 that killed more than 1,100 workers.

In China, poor working conditions were widely cited as contributing to suicides in recent years, such as at factories of Apple Inc supplier Hon Hai Precision Industry Co, also known as Foxconn, based in Taiwan.

"Respecting human rights and ensuring appropriate working conditions for the workers of our production partners are top priorities for Fast Retailing, and in this we are completely aligned with SACOM," Yukihiro Nitta, group executive officer responsible for Corporate Social Responsibility, said in a statement.

Fast Retailing said it had told Dongguan Tomwell Garment and Pacific (Panyu) Textiles to make various improvements in regulating working hours and their factories.

It also instructed Dongguan Tomwell Garment to establish a workers' union, hold elections and organize its first assembly in March, it said.

The company, however, said its inspection had found discrepancies with several points in SACOM's report regarding Pacific (Panyu) Textiles, including the fact that a worker's death was caused by electrocution.

It said it would continue its inspection and seek talks with SACOM for clarification.

Dongguan Tomwell Garment makes clothes for Uniqlo and Pacific (Panyu) Textiles supplies textiles to garment factories, including Dongguan Tomwell Garment. Neither company answered calls seeking comment.

SACOM declined to provide immediate comment.

Fast Retailing also said it would take steps to improve its monitoring system for its manufacturing partners including beefing up measures to check overtime hours, tracking such information as employee accidents and strikes, and introducing a system to monitor textile factories that supply garment plants.

Nitta said Fast Retailing would check progress within a month along with third parties including auditors.