Mandela Day on July 18 should be a public holiday, the Independent Municipal and Allied Trade Union (Imatu) said on Wednesday.
General secretary Johan Koen said the union had written to President Jacob Zuma stating its case for the day becoming an annual public holiday.
"Every year South Africans are reminded of the 67 years of his life that [Former President] Nelson Mandela gave fighting for the rights of humanity, equality, justice and democracy all South Africans enjoy today," Koen said in a statement.
On July 18, Mandela's birthday, people celebrate his contribution by spending 67 minutes doing something to help others.
Koen said if it was a public holiday, people could dedicate more than 67 minutes to worthy causes.
"Nelson Mandela is not only a living legend, but he also represents the qualities of compassion, determination and unity we must strive for as a nation to make a better South Africa for all."