The Credit Mobilier scandal of 1868 involved what industry?

The Credit Mobilier scandal involved the railroad industry. It specifically involved the Union Pacific Railroad Company. The Union Pacific was building railroads. This company created a construction company called the Credit Mobilier Company.  Many Congressmen received stock in this construction company.
The Credit Mobilier Company charged very high rates to build the railroads. These construction rates were very inflated. This allowed the stockholders to make a great deal of money. When word of this scandal broke, people weren’t happy that some Congressmen set up a scheme that would allow them to make huge profits. Two members of the House of Representatives were eventually censured for their role in the scandal.
While some railroad companies weren’t honest and were only concerned about making profits, James Hill, who ran the Great Northern, showed that a railroad company could make money without receiving any government help. 
https://www.history.com/topics/19th-century/credit-mobilier