Japanese clothing giant Uniqlo has failed to improve abusive working conditions or stop environmental pollution in its supplier factories in mainland China, despite having acknowledged the problems months ago, labor rights groups in the country said Thursday.

Four clothing factories manufacturing goods for the fashion chain were alleged to have abused workers by enforcing overtime work beyond legal limits, using toxic chemicals that harm the workers and pollute the environment and failing to pay for workers' social insurance and housing fund premiums, according to Sophie Chen, project officer for Students and Scholars Against Corporate Misbehavior (SACOM).

In a report jointly conducted by SACOM and three other labor-related groups and issued in January, the factories were also alleged to have collected fines from workers who failed to meet certain job requirements and ignoring workplace safety.