In the Compromise of 1850 California was admitted to the Union as a free state. In return, the South and slaveholding border states received a stronger fugitive slave law.
Congress had passed a fugitive slave law in 1793 to enforce Article 4, Section 2 of the United States Constitution, which read, "No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, but shall be delivered up on Claim of the Party to whom such Service or Labour may be due." But, with the rise of abolitionism, the Underground Railroad, and the significant number of successful slave escapes, especially from the border and upper-South states, it was believed by Southern slaveholders that a stronger law was needed.
The 1793 law had also been weakened by an 1842 Supreme Court case (Prigg v. Pennsylvania). Justice Joseph Story ruled that the federal law slave law was superior to state laws. But, with that being so, states were therefore not required to assist federal agents in returning slaves to their owners if state laws forbade it. This ruling thus allowed many states to introduce "personal liberty laws" that severely limited who could help federal marshalls capture runaways. It was believed by some Southern politicians that by giving in to California's wish to be admitted as a free state, a positive bargain could be made for a stricter fugitive slave law.
The 1850 fugitive slave law, authored and argued by Virginian James Murray Mason, stipulated that state and local authorities were indeed responsible for arresting and detaining slaves suspected of being runaways. If they did not, they were liable to be fined $1,000. Suspected slaves could not present testimony on their own behalf if arrested. This, of course, led to many abuses. Legitimate freedmen living in the North could potentially be arrested and sold into slavery since they could not provide testimony in court on their on behalf. In addition, if persons were caught aiding runaway slaves they too were liable to be fined $1000 and serve a six month sentence in prison. State and local authorities were paid for their successful arrests, and slave owners only needed to provide an affidavit to a federal marshall to have their slave pursued.
The law naturally delighted slaveholders and infuriated abolitionists and many previously otherwise unconcerned Northerners. Frederick Douglass claimed that, " Under this law the oaths of any two villains (the capturer and the claimant) are sufficient to confine a free man to slavery for life." Many in Congress felt that the law would not make a difference at all, and some supported it only to make the Compromise of 1850 work and keep the North and South somewhat pacified.
The law's impact was felt immediately. Many runaway slaves living as free men in the Northern states had to move on to Canada or risk being returned to slavery. Many northerners defied the law and increased their abolitionist activities and Underground Railroad support. The lack of enforcement of the law on the part of the Northern states would be one of the main points in South Carolina and other Southern states' reasons for secession. The Fugitive Slave Act of 1850 was one more log on the bonfire of sectional discord.