Two field studies tested the effects of a charge for single-use plastic bags recentlyimplemented in Buenos Aires City, Argentina. Study 1 showed a greater increase in consumers´ ownbag use after the charge was introduced in supermarkets where the policy was introduced, incomparison to control supermarkets where the charge was not introduced, or was introduced later intime. The effects were even stronger two months later. Study 2 analyzed factors underlying policysupport and own bag use six month after the charge was introduced. Policy supporters highlightedenvironmental benefits of the charge, while opponents stressed the financial costs. Moreover, mostconsumers indicated that they carried their own bags to protect the environment, suggesting thatintrinsic rather than extrinsic motivations caused behavioral changes. The theoretical and practicalimplications of the findings are discussed.