"Sapia has noted with concern reports that the SA Transport and Allied Workers' Union (Satawu) is embarking on a strike against Transnet from today [Monday]," the association said in a statement.
Sapia said it had spoken to its members about the strike and all had confirmed that appropriate contingency plans were in place to mitigate against possible fuel supply disruptions.
Sapia's members are BP Southern Africa, Chevron South Africa, Engen Petroleum, PetroSA, Sasol, Shell SA, and Total SA.
"While the full impact of the strike remains unclear, Sapia members will be closely monitoring the situation and endeavour to limit any inconvenience to the public," it said.
The Transnet strike began at 06:00 on Monday with about 18 000 Satawu members expected to down tools, according to the union.
Threats of a strike have been building for weeks as Satawu and another union, the United Transport and Allied Trade Union (Utatu), demanded a 15% across the board pay increase.
Transnet initially offered eight percent, but raised its offer to 11%.
Satawu rejected this, and opted to strike. Utatu was still consulting its members and expected an answer by Tuesday.
The company employs 50 000 people, 87% of whom are unionised. Utatu has 22 000 members working there.
- Sapa