A union representing about half the workers at power utility Eskom called off a strike over pay due to start on Wednesday at the state-owned firm after a court declared the planned industrial action illegal.
The South African Transport and Allied Workers Union (Satawu), which represents strikers in a pay dispute at the state-owned logistics group Transnet, said it had issued notices for sympathy actions at other transport and shipping firms.
The Transnet strike is already affecting ports and railways, and has held up exports of metals, cars, fruit and wine to Europe and Asia, as well as imports of vehicle parts and fuel supplies in Africa's biggest economy.
Satawu, with 39 percent of Transnet's 54,000 workers, wants its members, including employees of South African Airways, to join sympathy strikes to force Transnet to increase its pay offer.
It also asked workers at the country's coal export terminal to join the action, which is legal under South African laws.
"After further consultation with members it is the intention also to issue secondary strike notices on the Road Freight Association, whose members are road hauliers, as well as on aviation companies including SAA (South African Airways)," Satawu said in a statement issued late on Monday.
Fuel imports through South Africa to landlocked Botswana have been halved by the strike, and Botswana's energy minister was in Mozambique to try to secure long-term alternative supply routes through Maputo, government officials said.
Business Unity South Africa (BUSA) said each two-week period of the strike could cost the economy about 7 billion rand (£620 million) or 0.2 percent of gross domestic product.
"Supply chains are being severely disrupted and in many cases export contracts have been permanently lost. Retrenchments may now also be looming," the industry body said in a statement.
