The use of trading stamps grew with the spread of chain gasoline stations in the early 1910s and the then-new industry of chain supermarkets in the 1920s. Merchants found it more profitable to award them to all customers rather than cash only customers.[9] Legal challenges regarding the use of trading stamps were raised in various jurisdictions around the US but were often struck down.[2][10] Some merchant groups disliked trading stamps and actively worked to have them banned in their areas.[11] Following WWII the use of trading stamps expanded when supermarkets began issuing them.