The National Education Health and Allied Workers Union (Nehawu) has served the SA Revenue Service (SARS) with a letter saying it intends to strike next week Thursday.
Nehawu said earlier in the week it had failed to reach an agreement on wage negotiations with the revenue collection agency.
"The conciliation outcome was that the dispute remained unresolved and the certificate was then issued on the 19th March 2019," the letter reads.
Nehawu's demands include a salary increase of 11.4% and an increase to long-service awards to be increased with a percentage equal to its salary increase.
The notice follows long-standing differences between the union and SARS over employment conditions and benefits.
Khaya Xaba, Nehawu national spokesperson, told Fin24 on Friday that the union has 4 036 members at SARS.
SARS did not immediately reply to a request for comment.