United States ex rel. Dunlap v. Black, Commissioner of Pensions was a Supreme Court case that was decided in 1921. The case involved a dispute between the United States and the Commissioner of Pensions over the right of a veteran to receive a pension. The veteran, William Dunlap, had served in the Civil War and had applied for a pension in 1891. The Commissioner of Pensions denied his application, claiming that he had not served long enough to qualify for a pension. The Supreme Court ruled in favor of Dunlap, finding that the Commissioner of Pensions had acted arbitrarily and capriciously in denying Dunlap's application. The Court held that the Commissioner had failed to consider the evidence presented by Dunlap and had not given him a fair hearing. The Court also held that the Commissioner had failed to consider the fact that Dunlap had served in the Civil War and had been honorably discharged. The Court's decision in this case established the principle that veterans are entitled to a fair hearing when applying for a pension. The Court also established the principle that veterans should be given the benefit of the doubt when applying for a pension. This case is still cited today as an example of the importance of giving veterans a fair hearing when applying for a pension.

In United States Ex Rel. Dunlap v. Black, Commissioner of Pensions, the Supreme Court was asked to decide whether a veteran's widow could receive benefits from the government if her husband had been dishonorably discharged from service due to desertion. The majority opinion held that she was not eligible for such benefits because her husband’s discharge constituted an abandonment of his duty and thus did not qualify as honorable service under the relevant statute. Justice McReynolds wrote a dissenting opinion in which he argued that Congress intended for veterans' widows to be able to receive pension payments regardless of their husbands' discharges; therefore, it should have been up to Congress rather than the courts or executive branch officials like Commissioner Black who issued regulations on eligibility criteria for pensions, to determine whether or not someone is entitled to those payments based on their spouse's military record. He further noted that while desertion may constitute grounds for denying certain other types of relief available through federal programs such as disability compensation and back pay, this does not necessarily mean it should disqualify individuals from receiving pension payments meant specifically for veterans' widows since these are two distinct forms of assistance with different purposes and requirements attached thereto.