Why was the fugitive slave law of 1850 so controversial?

The Fugitive Slave Law of 1850 was controversial because it required citizens to assist in capturing and returning escaped slaves to their owners, even in free states. This law strengthened the institution of slavery and was seen as a violation of personal freedoms and due process rights for African Americans by many abolitionists and northerners. It intensified tensions between the North and the South, ultimately contributing to the onset of the Civil War.