ANC labour ally set to expel South Africa's biggest union

JOHANNESBURG (Reuters) - South Africa's biggest union faces expulsion on Friday from a labour federation linked to the ruling African National Congress (ANC), the biggest crack in a formal three-way alliance that has run the country since apartheid ended in 1994.

Delegates from the powerful Congress of South African Trade Unions (COSATU) were meeting in Johannesburg to cast ballots on whether or not to keep the National Union of Metalworkers of South Africa (NUMSA) in their ranks.

The governing coalition, referred to in South Africa as the "tripartite alliance", is comprised of the ANC, COSATU and the South African Communist Party.

Leaders of NUMSA, which has been pressing a militant left-wing agenda after falling out with the ANC over economic and labour policy, expect the union to be expelled from the federation, or at least temporarily suspended.

"We are on our way to the slaughter house," NUMSA president Andrew Chirwa told reporters ahead of the meeting.

NUMSA claims 340,000 members, mostly black, urban workers in sectors such as car manufacturing.

Its divorce from COSATU has been on the cards since last December, when it said it would not support the ANC in a May general election. The ruling party easily won, despite NUMSA's refusal to campaign.

NUMSA has said it plans to form a political movement called the "United Front" next month to push its socialist agenda.

Besides ideology, some other COSATU unions are upset at what they say are NUMSA's attempts to poach their members.