The law established commissioners to issue warrants for slaves who had run away and reached free states.
The Fugitive Slave Act was opposed by abolitionists, and was one of the inspirations for the novel Uncle Tom's Cabin.
Activists of the Underground Railroad had been helping slaves escape to freedom in the North before the passage of the Fugitive Slave Act. And when the new law was enacted it made helping slaves a violation of federal law.
Although the law was conceived as an effort to preserve the Union, citizens of southern states felt the law was not enforced vigorously, and that may have only intensified the desire of southern states to secede.

