In Connellsville and Southern Pennsylvania Railroad v. Baltimore, the Supreme Court of the United States was asked to decide whether a state could impose taxes on railroad companies that operated within its borders but also had lines extending into other states. The court held that such taxation was unconstitutional because it violated the Commerce Clause of the Constitution which grants Congress exclusive power over interstate commerce. Furthermore, since railroads are considered instrumentalities of interstate commerce, they should be free from any interference by individual states in their operations. This decision established an important precedent for protecting businesses engaged in interstate activities from discriminatory taxation imposed by individual states.

In Connellsville and Southern Pennsylvania Railroad v. Baltimore, the Supreme Court was asked to decide whether a state could tax property owned by another state in its jurisdiction. The majority opinion held that states have no power to tax the property of other states within their borders, as this would be an unconstitutional infringement on the sovereignty of those states. However, Justice Field dissented from this decision and argued that while it is true that one state cannot impose taxes upon another without violating constitutional principles, there are certain exceptions which allow for taxation when necessary for public safety or convenience. He further argued that since railroads were essential to interstate commerce at the time of this case, they should not be exempt from taxation simply because they are owned by another state; instead each individual railroad should be judged based on its own merits with regards to how much it contributes towards public safety or convenience in any given area where it operates.