Ex Parte Dugan was a United States Supreme Court case that addressed the issue of whether or not an individual could be held in contempt for failing to appear as a witness before a grand jury. The court ruled that such an action would constitute criminal contempt, and thus the individual could be punished accordingly. In this particular case, Dugan had been subpoenaed to testify before a grand jury but failed to do so without any reasonable excuse. As punishment for his failure to comply with the subpoena, he was sentenced by the district court judge to six months imprisonment and fined $500 dollars. On appeal however, it was argued that since there were no laws specifically prohibiting individuals from refusing service on juries or witnesses at trials then they should not be subject to criminal penalties either; instead civil remedies should suffice if necessary. The Supreme Court ultimately agreed with this argument and reversed Dugan's conviction holding that while Congress may have intended some form of punishment for those who fail their duty as jurors or witnesses it did not intend such punishments take on criminal forms which are more severe than civil ones.

In Ex Parte Dugan, the Supreme Court of the United States was asked to decide whether a writ of habeas corpus should be issued in favor of an individual who had been arrested and held without bail for alleged treason. The majority opinion denied the petition on grounds that it did not appear from the record that any legal cause existed for issuing such a writ. In his dissenting opinion, Justice David Davis argued that there were sufficient facts presented to warrant granting relief under habeas corpus. He noted that no charges had been filed against Dugan and he was being held solely on suspicion; thus, due process rights were violated by denying him access to counsel or other means of defending himself. Furthermore, Davis argued that if Congress intended treasonous acts as those which could be punished without trial then they would have explicitly stated so in their laws rather than leaving it open-ended as they did with this case. Therefore, he concluded that justice demanded granting relief through habeas corpus since all citizens are entitled to due process regardless of what crime is suspected or charged against them.