The Fugitive Slave Act in the 1850 Compromise was an extremely important law as it effected so many people around the country prior to the Civil War. This act basically demanded that any Federal marshall or law enforcement agent would be held responsible if they did not arrest an alleged runaway slave, regardless of proof. All that was required to determine that someone was allegedly a runaway slave was the testimony of one person.
If one person accused an African-American of being a slave that had run off, they would have to be arrested or the officer would be fined $1000. This made it virtually impossible for a black person to have any recourse in regards to someone maliciously accusing them of being a slave, and making it easy for someone to claim ownership of someone who was not their slave at all. The defendant was unable to ask for a jury trial and not entitled to testify for themselves.
The effects of this act were wide-reaching. The Underground Railroad, which was helping hundreds of slaves go north to escape slavery, now made their target destination as Canada in response to the Fugitive Slave Act. The north was also forced into being a defender of slavery in the south, so even in states where slavery was not allowed, their officers and the general public were held responsible for any escaped slaves that might come into their communities.
Abolitionists were forced to take an even deeper look at slavery because now their helping an escaped slave could result in a fine or even jail time as punishment. This forced many abolitionists to become even more outspoken against the institution of slavery and the Southerners that owned them. This act would spawn court cases and rulings as people struggled between the law and their own consciences, and it would remain in effect straight through the Civil War.