Gap has been accepted into the UK-based Ethical Trading Initiative (ETI), which promotes fair conditions for workers in fashion and food production.
Gap, which earlier this month announced plans to support a unionised factory in El Salvador, said joining ETI was an important step in improving conditions in garment factories around the world.
ETI ensures that conditions for workers producing clothes for the UK market meet international labour standards.
An ETI spokeswoman said Gap's efforts were significant: 'Gap has taken the decision to engage with the trade unions. We're pleased that it has seen ETI as the vehicle through which it starts to get involved.'
All companies go through a rigorous application procedure to join ETI, which means the board is convinced that Gap is committed to improving working conditions, she added.
Retailers including Marks & Spencer, Next, Debenhams and Asda are already ETI members.