Members of South Africa’s biggest union turned down a new pay offer from metals employers and are continuing a strike involving more than 220,000 workers in the manufacturing and engineering industries.

“Workers have rejected” the latest pay offer from the Steel and Engineering Industries Federation of Southern Africa, Andrew Chirwa, president of the National Union of Metalworkers of South Africa, said by mobile phone. Numsa, as the union is known, is seeking a one-year deal while the employers are pushing for a three-year agreement, he said, while declining to disclose further details.

The strike is set to enter its third week after the failure of the latest talks, which were mediated by the government. The stoppage is costing the industry about 300 million rand a day ($28 million), according to Seifsa, as the employers’ lobby is known. The strike is affecting as many as 12,000 companies including Nampak Ltd., Africa’s biggest can manufacturer, carmakers including General Motors Co. and Evraz Highveld Steel.

“We have not heard officially from Numsa,” Ollie Madlala, spokeswoman for Seifsa, said by phone. “We can’t really comment at this stage because they haven’t said anything to us.”

The union has revised its wage demand to a 12 percent increase from 15 percent, according to Chirwa. Seifsa last week raised its offer to 10 percent for the lowest paid workers. South Africa’s inflation accelerated to 6.6 percent in May.

There is a danger that the impact of the strike on South Africa’s economy could “break the camel’s back,” Henk Langenhoven, chief economist at Seifsa, said in an e-mailed statement yesterday. “South Africa cannot afford the current vicious declining spiral impacting the auto, mining and construction sectors and the overall economy.”

The rand, the currency of Africa’s second-biggest economy, weakened 0.2 percent to 10.7180 per dollar as of 11:10 a.m. in Johannesburg.