ABSTRACT Mexican Americans who live in the U.S.-Mexico border region suffer disproportionately from preventable cardiometabolic diseases. Regular brisk walking is an effective measure in regulating metabolic processes and preventing disease. Employer-based wellness programs are promising strategies to address this public health problem because they take advantage of workplace environments to improve opportunities for MVPA engagement while also addressing barriers associated with inactivity. Employer-based MVPA programs have not been widely tested on the U.S.-Mexico border. We plan to conduct a clustered Sequential Multiple Assignment Randomized Trial (SMART) to determine the effectiveness of an employer-based walking challenge intervention- 50,000 for Life (50K4Life)- in improving brisk walking engagement (at least 7,000 steps/day) among school district employees. The proposed intervention strategies are based on the walking interventions conducted by PI Salinas in El Paso and behavioral, environmental and worksite interventions by the Co-Investigators. The trial will include 30 randomly selected public schools with predominantly Mexican American employees from El Paso County area school districts. The intervention strategies in 50K4Life will be in two phases: 1) 50K4Life vs. 50K4Life + SMS text messaging and 2) Individual vs. School level adaptation for campuses with a low response to the initial intervention phase. We hypothesize that walking challenges with multilevel capacity building and adaptations based on intervention response will lead to improved adherence to PA guidelines. This proposed socio- ecological model-based study leverages resources through Hispanic Serving Institutions (HSI) from Texas and expertise in employer-based workplace interventions from the University of Georgia (UGA) based on the partner's accumulative work to address the disparity in PA and advance health equity in the Mexican American population. As part of our intervention evaluation, we will conduct a process evaluation and cost-effectiveness to provide insight into cost and scalability. This study will provide needed information on optimizing the implementation of evidence-based behavioral interventions to improve walking engagement among Mexican Americans living in the U.S.-Mexico border region.