The United States recently mandated disclosure labels on all foods that contain genetically modified organisms (GMOs), despite longstanding, widespread use of voluntary third-party non-GMO labeling. We leverage the earlier passage and implementation of a mandatory GMO labeling law in Vermont as a quasi-natural experiment to show that adding this mandatory labeling into a market with pre-existing voluntary non-GMO labels had no effect on demand. Instead, the legislative process made consumers aware of GMO topics and increased non-GMO product sales before the GMO labeling mandate went into effect. The GMO-related legislative processes also increased non-GMO product demand in other states that considered, but did not implement, GMO labeling mandates. We find that 36% of new non-GMO product adoption can be explained by differences in consumer awareness tied to legislative activity. Our findings suggest that voluntary non-GMO labels may have provided an efficient disclosure mechanism without mandatory GMO labels.