Excerpts from Books and Wikipedia
"Southern resentment of this situation led to passage of the Fugitive Slave Act of 1850, establishing a federal bureaucracy to enforce rendition. Abolitionists responded to the new legislation with ever more drastic rescue measures. Harriet Tubman, the most famous conductor on the underground railroad and a refuge herself, began her rescue work in the 1850s. The Transcendentalist intellectuals encouraged and endorsed resistance to the hated law. Thoreau succored an escaped slave at Walden Pond and fervently denounced the power of 'Slavery in Massachusetts'; Emerson inspired Yankee abolitionists to try to free the fugitive Anthony Burns from custody in 1854;" [Howe: Howe: What Hath God Wrought, p. 654]