As the number of skilled tradespeople dwindles in the U.S., Walmart is building up its own workforce to keep conveyor belts moving and refrigerated grocery cases cold. The nation’s largest retailer and private employer revamped its training program last year to increase the pipeline of maintenance technicians who work at Walmart's distribution centers and stores. inside and outside of the company. Analysts and employers say retirements and reduced immigration have worsened a shortage of carpenters, mechanics and other tradespeople that many industries need. Walmart says maintenance technicians are crucial to keeping its operations running smoothly, especially during the busy holiday season.