Traid, which collects and sells second-hand clothing, has already supplied pre-worn T-shirts to overseas poverty charity the Otesha Project for a sustainable cycling fundraising tour.
"We've got an extremely high volume of clothing passing through here, and a team of expert clothing sorters, who could, for example, pull out 100 pink T-shirts for a breast cancer charity," said a Traid spokeswoman.
"Otesha is extremely interested in reducing its carbon footprint, so its supporters are the type of people who would view this as a positive thing," the spokeswoman said. "We can see that this isn't for everyone."
She said some groups, such as student fundraisers, would benefit from not having to spend money on brand new T-shirts.