The charity is encouraging shoppers to employ consumer power and ask high-street stores where their clothes are made and, crucially, how workers' rights and safety are guaranteed.
Research shows that "rag trade" workers - mainly women - suffer some of the worst conditions and abuses, which often lead to poor health. In return for long hours, no job security, intimidation and harassment, many workers remain trapped in poverty on pay too low to meet basic needs.
From Guatemala to Pakistan, Bangladesh to the Philippines, surveys found overcrowded, noisy, hot, dark and dirty factories. According to Oxfam, workers are sacked and laid off without notice, time off is rarely allowed even for illness, overtime is compulsory and work- related health problems - such as eyestrain, headaches, chest and back pain, respiratory problem and skin infections - are universal. In many countries where there is extreme poverty, children are forced to work in factories.
Oxfam claims that the drive for cheaper production and shorter delivery times has encouraged human rights abuses of factory workers, and of those who do piece-work at home.
"Their treatment by the garments industry is an affront to their human dignity and an infringement of their basic rights," says its report published today.
It says that the power to improve working conditions for the millions employed in the industry rests with the high-street shops. Oxfam says many have little first-hand knowledge about conditions in the factories supplying their goods. Complex supply chains involving several manufacturers on the way to the stores have allowed exploitation and abuse to go unchecked.
Today, it is calling upon five of Britain's top high-street retailers - Burtons, C&A, Marks & Spencer, Next and Sears, to say where and under what conditions their garments are made.
Oxfam is not accusing any companies of using sweated labour, only asking them to prove that they have sufficient safeguards in place to ensure that they are not. All five (and some others) were approached by the Independent and all were confident that their practices ensured their factories were sound - although not all carried out independent inspections.
Oxfam accepts that many leading retailers are taking steps to guard against exploitation, but says they need to do more. Its campaign comes hard on the heels of that of another charity, Christian Aid, which recently revealed worker exploitation in the lucrative training-shoes trade.
Oxfam is also calling for independent monitoring of suppliers, as well as stronger international trade and labour regulations to improve the lot of the garment makers.
The charity is, however, anxious that its campaign does not precipitate a boycott or any hasty action from retailers that could lead to factories closing down altogether or to children - who often support poor families - being thrown out of work. They say that would damage those working in the industry even more.
"Ending child labour requires a long-term strategy aimed at eradicating the conditions of poverty and inadequate employment opportunities for adults which make it necessary," the report concludes.