The citation for this case is 75 US [8 Wallace] 603.
You can find the genesis of this case in the first Legal Tender Act, approved February 25, 1862 [12 US Stat. 345], which authorized the US Government to issue paper money that was not redeemable in gold or silver. This money was known as “greenbacks” and was to be considered legal tender for all debts. This meant creditors had no choice but to accept the greenbacks in payment rather than demanding only gold or silver money. This was one of the ways the US Government paid for the Civil War. “Historically, legal tender had been the hallmark of an irredeemable, deteriorating paper money. The framers of the Constitution clearly intended to banish it from the American scene. Reflecting this view, Chief Justice John Marshall excoriated legal tender. In 1862, the legal tender statute was seen as a temporary, if unfortunate, expedient. The doctrine of implied powers, derived from the war and borrowing authority, was repeatedly invoked in Congress to justify the legal tender quality of greenback dollars.” [Gerald T. Dunne, “Legal Tender Cases,” in Kermit L. Hall, ed., The Oxford Guide to United States Supreme Court Decisions, p. 158] During Reconstruction, Congress sought to protect the Reconstruction Acts and reduce President Andrew Johnson’s ability to interfere, and one way they did this was to limit the number of justices on the Court so Johnson couldn’t appoint justices that shared his philosophy. In an act passed on July 23, 1866 [14 US Stat. 209], Congress said the President could not appoint any justices until the number of justices, not counting the Chief Justice, was reduced to six. Justice John Catron had died on May 30, 1865 so the Court had nine justices at the time, including Chief Justice Chase. Justice James M. Wayne died on July 5, 1867, bringing the total justices down to eight. When Ulysses S. Grant took office as the 18th President of the United States, Congress passed another act, the Judiciary Act of April 10, 1869 [16 US Stat. 44], which increased the Court to nine justices. Thus the Court consisted of eight justices when it heard Hepburn v. Griswold on December 10, 1869, and Grant had to appoint one more justice. This was the first of the three cases known collectively as the “Legal Tender Cases” [See articles here, here, and here].
“The case involved a couple, Susan P. and Henry H. P. Hepburn, and a man named Henry A. Griswold. On June 20, 1860, the Hepburns gave Griswold a promissory note with a due date of February 20, 1862. Following the passage of the act of February 25, 1862, which made greenbacks legal tender for the payments of all debts, the Hepburns tried to give Griswold greenbacks in the face amount of the debt to pay the note in full. This greatly upset Griswold, because when he made the loan to the Hepburns, he expected to be paid in specie. If he accepted greenbacks in payment, he would have substantially discounted his note from its face value. Griswold refused to accept the greenbacks in payment and sued the Hepburns for payment in specie. The case was filed in the Louisville Chancery Court in Kentucky.” [Robert Bruce Murray, Legal Cases of the Civil War, p. 102] That court sided with the Hepburns and Griswold appealed. The Appeals Court reversed the Chancery Court, siding with Griswold. The Hepburns then appealed to the Supreme Court. After the arguments the justices met to decide the case, and the vote was tied 4-4. Then Justice Robert C. Greer changed his vote to side with those who wanted to declare the Legal Tender Acts unconstitutional, making a 5-3 decision. Justice Greer resigned from the Court on January 31, 1870. Chief Justice Chase wrote the majority opinion, which he delivered on Feburary 7, 1870, a week after Greer left the Court. Thus the actual vote was 4-3, with Chase and Field voting with the majority and Swayne, Miller, and Davis dissenting.
Chase, who was Secretary of the Treasury in 1862 and only reluctantly supported the Legal Tender Act, wrote, “We are obliged to conclude that an act making mere promises to pay dollars a legal tender in payment of debts previously contracted, is not a means appropriate, plainly adapted, really calculated to carry into effect any express power vested in Congress, that such an act is inconsistent with the spirit of the Constitution, and that it is prohibited by the Constitution.” [75 US 603, 625] In a paragraph he no doubt used to explain his own actions, Chase wrote, “It is not surprising that amid the tumult of the late civil war, and under the influence of apprehensions for the safety of the Republic almost universal, different views, never before entertained by American statesmen or jurists, were adopted by many. The time was not favorable to considerate reflection upon the constitutional limits of legislative or executive authority. If power was assumed from patriotic motives, the assumption found ready justification in patriotic hearts. Many who doubted yielded their doubts; many who did not doubt were silent. Some who were strongly averse to making government notes a legal tender felt themselves constrained to acquiesce in the views of the advocates of the measure. Not a few who then insisted upon its necessity, or acquiesced in that view, have, since the return of peace and under the influence of the calmer time, reconsidered their conclusions, and now concur in those which we have just announced. These conclusions seem to us to be fully sanctioned by the letter and spirit of the Constitution.” [75 US 603, 625-626]
This case held the Legal Tender Act to be unconstitutional, but it wasn’t the last word. With Greer’s resignation Grant had two Court appointments, and he made those two nominations on the same day Chase delivered his opinion. He nominated two stalwart Republicans, William Strong and Joseph P. Bradley, both of whom wanted very much to hear another legal tender case, which led eventually to the Court overturning the Hepburn v. Griswold ruling when those two justices joined the three dissenters in upholding the constitutionality of the Legal Tender Acts.