US labour rights activists have mounted a pre-holiday campaign calling on shoppers to boycott specialty-apparel retailer Gap Inc for producing clothing in what it called sweatshops and exploiting factory workers in developing countries.

A six-month investigation carried out by the Union of Needletrades, Industrial and Textile Employees documents "abusive working conditions" at 40 Gap-contracted clothing factories in Cambodia, Lesotho, Indonesia, Bangladesh, El Salvador and Mexico, UNITE officials told a New York news conference Wednesday.

Union spokesmen charged Gap with systematically driving down wages while simultaneously exploiting the people producing its goods, creating a system of oppression that has resulted in "the loss of human and labour rights and a decrease in the general quality of life."

The activists want consumers to boycott Gap products over the holiday period in an attempt to stop the retailer "exploiting sweatshop labour around the world," said union official Steve Weingarten. "We want them to pay a wage that allows a decent standard of living and allow workers to organize unions to improve conditions in their factories."

Also present at the press conference were workers from Lesotho, Indonesia and El Salvador, who detailed low salaries, long working hours, and sweatshop conditions at factories making Gap products.

Gap spokeswoman Stacy MacLean said the company "shares these concerns," and works with factories to maintain standards. The clothing retailer, which is one of the nation's largest, has a Global Compliance programme with 90 full-time staff who travel worldwide to monitor conditions in subcontractor factories making Gap clothes.