While fashion bosses receive huge salaries and bonuses, staff working for suppliers abroad are not earning enough to get out of poverty, said the campaign groups War on Want and Labour Behind the Label.
Supermodel Kate Moss was paid £3m for her work with Topshop while factory staff in Mauritius can expect to earn £64 for a month's work, according to the Let's Clean Up Fashion report.
And the individual salaries and bonuses paid to Tesco boss Sir Terry Leahy and Marks & Spencer chief executive Stuart Rose are the same as the combined annual wages of thousands of Bangladeshi and Sri Lankan clothing workers.
Staff in Bangladesh are paid 7% of a UK living wage, even when the cheaper cost of living is taken into account.
This compares to 9% of a UK living wage earned by the average garment worker in India, 11% in China and Vietnam, 14% in Thailand and 25% in Morocco.
Of the 34 well-known retailers surveyed, Gap, New Look and Next were named as the only ones with "genuine plans" to sort out pay and conditions for overseas workers.
Bringing in a living wage for overseas suppliers is achievable for UK fashion firms, the report said.
"The fashion industry has the means to sort this out, but at present the brands seem too busy blaming each other and making excuses to actually achieve the living wage," it added.
Campaigners want the Government to bring in laws making British firms enforce ethical labour standards throughout their supply chains.
Clothing firms have been urged to improve pay above and beyond minimum wages among their overseas suppliers.