In Parker v. Phetteplace et al., the Supreme Court of the United States held that a state court could not issue an injunction to prevent a federal officer from performing his official duties, even if those duties were in violation of state law. The case arose when two men, John and William Phetteplace, sought an injunction against Joseph Parker, who was appointed by President Lincoln as collector of internal revenue for the District of Columbia. The Phetteplaces argued that Parker's appointment violated Maryland law because he had not been approved by its legislature or governor prior to taking office. However, the Supreme Court found that such approval was unnecessary since it would interfere with Congress' power under Article I Section 8 Clause 1 (the Taxing and Spending Clause) to lay taxes and collect them without interference from any other branch or level of government. Furthermore, they noted that this power is exclusive; only Congress can determine how taxes are collected within its jurisdiction regardless of what any particular state may say on the matter.

In Parker v. Phetteplace et al., the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving two citizens of different states. The majority opinion held that it did, but Justice Field dissented from this ruling. He argued that under the Constitution, federal courts have exclusive jurisdiction in cases between citizens of different states and thus the state court lacked authority to hear such cases. Furthermore, he noted that Congress had not given any power to state courts in these matters and so they should be left for resolution by federal tribunals only. In conclusion, Justice Field believed that allowing state courts to adjudicate disputes between citizens of different states would lead to confusion and inconsistency among rulings across jurisdictions as well as an erosion of national unity on important questions concerning interstate commerce or other matters affecting more than one State at once.