The Fugitive Slave Act made it illegal for Northerners to assist an escaped slave seeking freedom. Like Sessions wants to force Californians to assist in the capture of immigrants, the Act compelled Northerners to actively participate in the hunt for blacks on pain of fine or imprisonment. Two Quakers were charged with treason for refusing to help slave hunters.
Several states passed laws forbidding state officers from helping the slave hunters. Massachusetts made it illegal for any state official to return a person fleeing slavery and disbarred any lawyer who represented slave masters.
The people, united, will never be defeated. ~ 1960's civil rights slogan