How did the railroad contribute to a sense of labor unrest, populism, and Gilded Age business changes?

The railroad companies often employed unskilled labor to build their tracks. This could be dangerous, underpaid work. When railroad workers went on strike, railroads called up investigators such as the Pinkerton Agency to arrest the organizers, and the strikers were replaced with scab labor.  This led to violence and was the root of the Railroad Strike of 1877 that paralyzed shipping in the eastern United States. The public was on the side of the workers until they started to destroy track and hinder mail service. After this, the public sided with management and the strike was quickly put down.
In the West, railroads charged high prices for farmers to move their crops to the markets in the East. They also controlled the markets as often only one railroad served a large area. This led to Congress intervening, citing their ability to regulate interstate commerce. Congress prohibited railroad price gouging. Farmers also organized in Grange organizations to ensure that they received fair prices for their crops as well as good rates to move the crops.