What did some Northern states do to oppose the Fugitive Slave Act?

Northern States were so angered by the Fugitive Slave Law, They passed special laws nullifying the law, participated in civil disobedience and helped slaves escape to Canada.

Many several northern states passed laws that nullified the fugitive slave laws. This nullification was similar to the nullification of the tariffs of 1828 by the southern states. These laws were unconstitutional and helped to justify the nullification and succession of the southern states.

When the slave catchers tried to ship captured slaves back to the south they were often opposed by mobs of angered abolitionists. It took over 1,000 soldiers to protect the slave catchers escorting an escaped slave in Boston.

The underground railroad that had helped slaves escape to the north now had to be extended to the bounder with Canada. Quakers in Pennsylvania were arrested fined and put in jail for helping slaves escape to Canada.

The actions of the northern states nullifying the law, ignoring the law, and engaging in civil disobedience directly disobeying the law rendered the Fugitive Slave Laws ineffective.