Numsa, with around 155,000 members organised in the sector, have been on strike since 5 October to press for higher wages, an action that could hit supplies of parts to make new cars and accessories.
On Monday, luxury car maker BMW said it lost production at its main vehicle assembly plant in South Africa when a number of suppliers were affected.
"Regrettably, at the conclusion of last night's meeting, we can report that we do not have an agreement," Lucio Trentini, chief executive at SEIFSA, told Reuters.
"We will regroup this morning and plot the way forward. The revised and improved offer has been rejected," he added, after Numsa took a revised offer to the members last week.
The strike was launched after wage talks hit a deadlock and arbitration failed, with Numsa demanding an 8% across-the-board wage rise in the first year, and inflation plus 2% for the second and third years.
SEIFSA had offered 4.4% for 2021, inflation plus 0.5% in 2022 and inflation plus 1% in the third year.
A Numsa spokesperson did not comment and said the group planned to have a media briefing later in the day.
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