The following is from Wikipedia:

The Washington Terminal Company is a corporation created in Washington, D.C. to provide support to railroads using Washington's Union Station. It was established in 1901 by the Baltimore and Ohio Railroad and the Pennsylvania Railroad-controlled Philadelphia, Baltimore and Washington Railroad. Today, its operations are run by Amtrak. 

The Washington Terminal Company owned and operated Union station (opened in 1907) and about 5 miles (8.0 km) of track in the Washington area, providing switching services for passenger trains using the station or passing through the area:

  • Baltimore and Ohio Railroad (B&O)
  • Pennsylvania Railroad (PRR)
  • Chesapeake and Ohio Railway (C&O)
  • Richmond, Fredericksburg and Potomac Railroad (RF&P)
  • Southern Railway (SOU)
  • Atlantic Coast Line Railroad (ACL)
  • Seaboard Air Line Railroad (SAL)

In 1981, Amtrak took over the terminal company's operations. Still, the Washington Terminal Company remains a separate legal entity, and unlike Amtrak, it is not exempt from the Interstate Commerce Act. This allowed Virginia Railway Express to threaten a filing to the Surface Transportation Board to enforce its right to access when Amtrak tried to oust VRE from Union Station after VRE said they would not automatically re-hire Amtrak as its operating contractor.