In Astrup v. Immigration and Naturalization Service, the Supreme Court ruled in 1970 that a Danish immigrant could not be deported for refusing to serve in the U.S military due to his conscientious objector status. The case involved Jorgen Astrup who had been ordered by immigration authorities to leave the country because he refused induction into the armed forces as required under an agreement between Denmark and United States which allowed him entry into America for permanent residence. However, Astrup argued that his refusal was based on deeply held religious beliefs against war and violence, making him a conscientious objector protected under U.S law from forced military service. The court agreed with Astrup's argument stating that it would be inconsistent with American principles of justice and international comity if immigrants were compelled to violate their conscience or face deportation.

In the dissenting opinion for Astrup v. Immigration and Naturalization Service, Justice Harlan argued that the Court's decision was a misinterpretation of Section 241(a)(6) of the Immigration and Nationality Act. He believed that Congress intended to exclude from deportation those who had been convicted of crimes involving moral turpitude only if they were sentenced to less than one year in prison or fined less than $1,000. The majority's interpretation would allow anyone with multiple convictions but no single sentence over one year to avoid deportation, which he felt contradicted Congressional intent. Furthermore, he disagreed with their reliance on legislative history rather than clear statutory language as a basis for their ruling.