TOKYO -- Japanese fashion empire Fast Retailing Co. says it will expand monitoring of its suppliers following complaints over labour violations and other problems.

Yukihiro Nitta, who is in charge of corporate social responsibility at the fashion giant, said Wednesday the company's oversight would extend to the fabric manufacturers who supply the garment companies that make clothes for Fast Retailing.

The company plans to have a pilot program involving 30 per cent of the fabrics used in Uniqlo clothing in place by the end of March, and to expand it to all of its textile suppliers by March 2016.

Tadashi Yanai, the founder of Fast Retailing, is reported to be the richest man in Japan, with wealth estimated by business magazine Forbes at $17.8 billion as of April 2014. He has parlayed the men's clothing store his father started in a western Japanese mining town into a global garment empire employing more than 30,400 workers.

But the company's low-cost, high fashion production model faces is challenged by rising wages in China, obliging it to operate in lower-cost countries such as Cambodia and Bangladesh, where managing conditions at factories could prove more daunting.

Yanai has set a goal of generating 5 trillion yen ($42 billion) in annual sales by 2020, seeking to surpass rivals like Gap Inc. and Spain's Inditex SA, which owns the Zara brand.

The company earlier announced broad plans to tighten controls on working hours and other conditions for workers at factories that are mostly in developing countries such as China, Vietnam, Cambodia and Bangladesh. That followed a report by labour rights groups detailing specific problems at two factories in southern China.

Fast Retailing said it has taken specific measures with those suppliers to ensure working hours, air quality, temperatures and other working conditions will meet its standards.

The company said it also will increase surprise audits of indirect suppliers such as textile makers and conduct training on labour rights for workers and managers.

"We believe that respect for human rights and ensuring fair working conditions are top priorities for the entire industry, and not just Fast Retailing," said Nitta, the corporate social responsibility executive.