Workers from the National Union of Metalworkers of SA. File photo: Mogomotsi Magome.

Johannesburg - A scheduled strike tomorrow by 220,000 members of a South African metalworkers’ union could cripple the economy because the industries at risk comprise about four percent of the gross domestic product, Citigroup said.

“Depending on the length of the strike, the GDP impact could be severe,” Gina Schoeman, an economist at Citigroup in Johannesburg, said today in an e-mailed note to clients.

The strike may last at least one month, and if it does, third- quarter GDP has a “substantial risk of falling negative again.”

Africa’s second-largest economy contracted 0.6 percent in the three months through March as a 22-week long strike at the country’s platinum mines that ended last week led to a 25 percent slump in mining output.

Mining comprise 5 percent of GDP and manufacturing about 15 percent.

The National Union of Metalworkers of South Africa is waiting for employers to meet “double-digit” wage increase demands, Mphumzi Maqungo, national treasurer of the union, said today on Johannesburg-based radio station Power FM.

The union is demanding a 12 percent raise for metals and engineering workers, while employers have proposed a three-year deal that includes increases of as much as 8 percent the first year.

A protracted strike at metals manufacturers would affect exports and lead to a substantial widening of the shortfall on the current account in the third quarter, Schoeman said.

“If production is offline for even a month, the likely impact on exports is meaningful, particularly as about 40 percent of export goods are related to the sectors that would be impacted by the strike,” she said. - Bloomberg News