The Independent newspaper alleged that the clothing being made for the London 2012 Olympics was "being manufactured for Adidas in sweatshop conditions in Indonesia, making a mockery of claims by London 2012 organisers that this summer's Games will be the most ethical ever".
Adidas, the German sportswear and equipment manufacturer, is investigating, the London organising committee said.
"We place a high priority on environmental, social and ethical issues when securing goods and services and take these allegations extremely seriously," said a spokeswoman.
"We have spoken to Adidas and they have assured us that they are investigating these allegations, the conclusions of which will be made public.
"We regularly remind all of our licensees of the importance we place on the sustainable sourcing code they have each signed up to."
Workers at nine Indonesian factories which have contracts to produce Olympic shoes and clothing for Adidas are working up to 65-hour weeks and earning as little as 5,000 rupiah ($0.55, 42 euro cents) an hour, the report claimed.
The Commission for a Sustainable London 2012, the body responsible for monitoring ethical practices relating to the Games, told The Independent that it was "deeply concerned" by the report.
The organising committee's priority "must be to investigate these issues and act accordingly to protect workers' rights and improve working conditions," said Shaun McCarthy, the commission's chairman.
The Independent said in its editorial that the working conditions reported by staff at the Indonesian factories were "unconscionable".
"Workers tell of pitiful wages, unreasonable production targets, appalling hours and even outright abuse," it said.
The London Games organisers "should be ashamed" of themselves, it added.
Last month fashion designer Stella McCartney revealed the Union Jack-inspired outfits she has designed for the British Olympic team at a glitzy London launch.
The 2012 Olympics run from July 27 to August 12.