Hillary Clinton is asking for votes from workers collecting their pay checks at a longshoreman's hall in Charleston, South Carolina ahead of the state's Democratic presidential primary.
Clinton thanked the union for its endorsement and said she needs the help of its workers on Saturday.
She pledged to the predominantly black crowd that she would build on the "progress" that President Barack Obama, the nation's first black president, has made.
Clinton added that she wants to "make sure we don't take any risks and have that progress ripped away."
Earlier Wednesday, Clinton visited a residential program that helps rehabilitate criminals and substance abusers in North Charleston. She and rival Bernie Sanders are both pledging to reform the criminal justice system.