Front-of-pack labeling (FOPL) is a tool that enables consumers to compare foods and select healthier options. Due to low understanding of the Guideline Daily Amount (GDA) labeling among Mexicans, a law was implemented in October 2020 that modified the FOPL to a warning labeling (WL) system. The purpose of this study was to compare the perception and understanding of GDA and WL during the law modification period. We conducted a panel design with two measurements: (1) using GDA label (September 2020) and (2) using WL (October-November). We estimated differences in GDA vs. WL through multinomial logistic regression models and changes were measured through predictive margin contrasts and Wald tests. When comparing the same products with different labels, the participants reported that it would be unlikely/very unlikely that they would consume products packaged with the WL (81.5%; 95%CI: 79.2, 83.8) compared to those with GDA (24.2%; 95%CI: 21.7, 26.7). Consumers' perception was that the quantities of packaged products they should consume was small or very small when they used the WL (93.8%; 95%CI: 92.4, 95.5) compared to GDA (41.6%; 95%CI: 39.7, 44.6). When comparing food groups, participants were more confident about choosing healthy products when using the WL compared to the GDA. During the implementation of WL in Mexico, the studied population had a better perception and understanding of less healthy packaged foods when using WL, compared to the GDA label.