Updated at 2016-01-31 07:29:34 UTC
Andrew Morgan spent two years making "The True Cost" to explore the impact fast fashion is having on the world, after being shocked by the deadliest garment factory accident in history - the collapse of Rana Plaza in Dhaka in Bangladesh.
More than 1,100 people were killed when the eight-storey building collapsed in April 2013, highlighting the bleak conditions facing millions of workers in poor countries producing garments for Western retailers.
Morgan, a U.S. filmmaker, said it was startling that more than 400 percent more clothing is made now than 20 years ago, with 97 percent outsourced to poor nations where factory owners compete on price for contracts and regulation is lax.
He said the workers need these jobs but many are paid a minimal wage and have little job security, while their health is affected by the chemicals used to produce the cheap fabrics made into T-shirts that are snapped up for $5 in Western stores.
"We have to get past the smokescreen, we have to change the system," Morgan told a panel discussion in London after a screening of the film.
"The message is not to people to stop buying or to stop loving the things you wear but ... to slow down the endless treadmill of buying disposable, cheap clothing."
The film looks at how the fashion industry starts in cotton fields in India and the United States, moves to factories in nations like Bangladesh and China supported by an army of about 40 million, mainly female workers, then ends up in Western stores.
Morgan also focused on the environmental impact of the industry with discarded clothing piling up in landfills and chemical runoff from factories.
Livia Firth, an executive producer on the film and creative director of sustainability brand consultancy Eco-Age, said there was no single, easy way to improve the industry but said a transnational agreement on wages and conditions would help.
"We consumers have the power ... We are in charge," said Firth, highlighting innovative ways employed by some brands and companies to produce fashion without exploiting workers or harming the environment.
British fashion designer Stella McCartney said it was time the industry changed and she no longer looked at just style.