The City of Cape Town will be worst hit by a nationwide strike by workers who process traffic fines, the SA Municipal Workers' Union (Samwu) said on Friday.

It said the "more than 80 percent" of Syntell (Pty) Ltd's workforce who were Samwu members would down tools next week.

This followed a failed attempt at mediation, and the company's unilateral implementation of a five percent wage increase.

"To make matters worse, this company is owned by a trade union investment company (Sactwu Investment Holdings)," Samwu said in a statement.

It said the strike was likely to "negatively impact" on the processing of traffic fines and summonses throughout the country.

"This as Syntell has contracts with most municipalities to run their traffic functions.

"The City of Cape Town, one of the biggest municipalities that outsourced traffic services to Syntell, will be the worst affected by the strike action."

Syntell, which has its head office in Cape Town, was not immediately available for comment.