One of the main goals of the populist movement in the late 1800s was the regulation of railroads.
The populist movement was dominated by farmers. They felt that they were being abused by rich and powerful interests in the business community. One of the most important of these was railroads. They felt that the railroads charged them rates that were much too high to ship their products to market. The railroads (the populists said) knew that the farmers had no other way to move their crops and therefore charged the farmers very high prices.
For this reason, a major goal of the populists was the regulation of railroads. They wanted the government to prevent the railroads from charging them what they saw as excessively high prices.