The training focuses on assisting Sainsbury's suppliers in identifying whether hidden exploitative practices exist at the farms, pack houses, processing plants and factories throughout the global supply-chain.
This training pilots this week with GLA officers providing a package that has been developed to meet the specific requirements of the Sainsbury's product suppliers.
GLA chief executive Paul Broadbent said: "We are delighted to have forged this industry leading agreement and to work alongside Sainsbury's in this way.
"There is a real commitment and desire on both sides to identify any practice that subjects workers to exploitation.
"Such activity, by its very nature, is kept hidden by its perpetrators as far as possible and is difficult to detect but there are indicators to look out for and these are what we will be teaching Sainsbury's product suppliers to spot.
"By raising awareness through training, Sainsbury's is showing a determination to identify any issues of concern. I applaud them for this and will continue to work alongside them to tackle it."
This new training arrangement builds upon the GLA's Supplier/Retail Protocol that was
launched in October 2013 by Home Secretary Theresa May.
The protocol was a commitment from major retailers and suppliers to share information and intelligence with the authority about suspicions and wrongdoings with confidence.