What was the fugitive slave act? why did this anger northerners?

I might have got it mixed up but the northerners were slave owner and the fugitive slave act was an act to get rid of slavery.  It angered the northerners because it would mean they will either one pay the african americans or two let them be free. 

not entirely postive i might have got it mixed up with northerners or southerners but i hope im right 

hope this help

Sir thomas more, venerated in the catholic church as saint thomas more, was an english lawyer, social philosopher, author, statesman, and noted renaissance humanist. he was also a councillor to henry viii, and lord high chancellor of england from october 1529 to 16 may 1532. i found this information on wikipedia