In the case of DeGregory v. Attorney General of New Hampshire, 1965, Paul DeGregory was subpoenaed by the state's attorney general to testify in an investigation into subversive activities under a state statute. When he refused to answer certain questions about his affiliations with the Communist Party on grounds that it violated his First Amendment rights and could potentially incriminate him (Fifth Amendment), he was convicted for contempt. The Supreme Court ruled in favor of DeGregory, stating that while states have power to investigate potential threats to their government, they cannot infringe upon citizens' constitutional rights during such investigations. This means that compelling individuals to disclose their political associations without proper justification is unconstitutional as it violates freedom of speech and assembly protected under the First Amendment.

In the dissenting opinion for DeGregory v. Attorney General of New Hampshire, Justice Harlan argued that the majority's decision was a departure from established principles regarding legislative investigations. He contended that such inquiries are an essential part of the legislative process and should not be subjected to judicial interference unless there is clear evidence of abuse or violation of constitutional rights. In this case, he believed no such violations had occurred. The questions asked by the committee were relevant to its investigation into subversive activities and did not infringe on DeGregory's First Amendment rights as they were related to his political associations rather than his beliefs or opinions. Furthermore, Justice Harlan expressed concern about potential chilling effects on future legislative investigations due to fears of judicial intervention based on subjective assessments of relevance and pertinency.