Johannesburg: About 70,000 workers seeking double-digit wage increases at South Africa's petrol stations, garages and auto dealerships planned to walk off the job on Wednesday, threatening to widen strikes in Africa's largest economy.

Unions representing about 1.3 million state workers, who have been on a three-week strike, were expected to announce on Wednesday afternoon if they would accept a new government wage offer designed to end the action that has shut schools and caused chaos at hospitals.

Financial traders said the state workers' strike had hurt sentiment but so far had had no major impact on bonds or the rand currency. One prominent economist said the strike had cost the economy about $150 million a day.

Observers say fresh strike action by workers in the automotive service sector could affect petrol supplies. At many petrol stations around Johannesburg, attendants were on the job but were not in uniform, with several saying they feared intimidation.

The union representing the sector said workers wanted a 20 per cent wage increase - five times the inflation rate of 3.7 per cent in July.

Investors also are worried about a one-day strike planned by all the unions in the country's largest labour federation COSATU, which claims it has million members and more than 20 union affiliates, who would go out in sympathy with the state workers.

Labour action on Thursday could affect mining, manufacturing and other key industries.

A one-day strike was thought to not likely have too much impact, but a prolonged strike would further hurt the economy if there is no resolution to the state workers' strike, COSATU has said.

The government has offered state workers, including teachers, nurses, customs officials and office clerks, a pay rise of 7.5 per cent and 800 rand ($108.50 or Dh662) a month for housing. The unions are demanding an 8.6 per cent rise and 1,000 rand.

The coalition of more than a dozen unions representing state workers was expected to announce a collective decision on whether to accept the new offer on Wednesday afternoon.

Some groups may announce the results of the votes of their membership ahead of that time.

Observers have said the government probably would be forced to make cuts elsewhere and borrow money to pay for the wage package for the state workers, making it more difficult to meet its goal of cutting a deficit of 6.7 per cent of GDP.

The strikes have presented President Jacob Zuma with one of his most difficult policy problems since taking office and strained a long-standing governing alliance with the COSATU.