United Food and Commercial Workers Local 400 will represent the campaign workers as Sanders, an independent US senator from Vermont, seeks the 2020 Democratic nomination.
Sanders, who is 77, visited a walk-in clinic "out of precaution", in SC after falling and injuring himself on the glass door of a shower, according to campaign spokesperson Arianna Jones.
The rally will be held Saturday.
"We can not just support unions with words, we must back it up with actions", Sanders said. On the campaign trail, Sanders has repeatedly vowed in speeches - as he did in 2016 - to make it easier for workers to unionize, often tying it to his push for a rise in the minimum wage to at least $15 an hour. In card check, union organizers ask workers to sign cards affirming that they support a union.
However, his campaign has recently come under scrutiny for alleged instances of sexual harassment by senior staffers during the 2016 campaign. In February, the politician announced he will again run for president in 2020.
Local 400 represents 35,000 members in the retail food, health care, retail, food processing, service and other industries in six states and D.C., according to the group. The campaign said that the United Food and Commercial Workers Local 400 had been chosen by the majority of the bargaining employees to serve as their exclusive representative.