Unisa's campus in Sunnyside, Pretoria, was closed on Thursday because of a pay strike, a spokesman said.
"Our campus in Sunnyside has released staff for the day," University of SA spokesman Martin Ramotshela said.
"The reason was for precautionary measures because of reports of intimidation by striking workers."
Ramotshela said most workers could not enter the campus because the entrance was blocked.
National Education, Health, and Allied Workers' Union and the Academic and Professional Staff Association Union members at the university went on strike after rejecting the five-percent salary increase it tabled.