In 2022, all foods for sale in the US will be required to carry disclosure labels if they contain ingredients with genetically modified organisms (GMOs). While this is a significant change to labeling requirements, voluntary non-GMO labels already exist to facilitate consumer choice. Past legislative and voter-initiated measures in several states have proposed mandatory GMO labeling, with Vermont being the only state to successfully pass and implement such a law. We leverage a novel dataset from the Non-GMO Project to examine the direct effect of mandatory GMO labeling and the indirect effect of the associated legislative process on demand for voluntarily-labeled non-GMO products. We show that the legislative process heightened consumer awareness of GMO topics and increased adoption of products with voluntary non-GMO labels, even absent actual implementation of mandatory GMO labeling: about one-third of new non-GMO product adoption is explained by the local information environment. We then utilize implementation of the mandatory GMO labeling law in Vermont as a quasi-experiment to show that in the presence of existing voluntary non-GMO labels, mandatory labeling did not have any additional effect on demand. Our findings suggest that voluntary non-GMO labels may already provide an efficient disclosure mechanism without mandatory GMO labels.