Johannesburg - The National Union of Metalworkers of SA is severing ties with the ruling alliance comprising the ANC, the Congress of SA Trade Unions (Cosatu) and the South African Communist Party (SACP).



It said on Monday that it will launch a socialist united front as soon as December.



"We decided to break with the alliance and we resolved to form a United Front and explore the possibility for socialism in South Africa," the Numsa said in a statement.



But Numsa said it did not plan to voluntarily leave Cosatu.



Cosatu last week postponed a vote to expel Numsa, which has been pursuing a left-wing agenda after falling out with President Jacob Zuma over economic and labour policy.



Some Cosatu unions are also upset at Numsa's attempts to "poach" their members.



Numsa is the biggest union in the country with over 340 000 members.



At a special meeting in December last year, Numsa resolved to withdraw its support for the ANC in the May general elections.



Look at some of the reactions on Twitter:



Numsa is playing a very dangerous game. Empa good luck on going alone. — Pholoho Selebano (@Pholoho) October 27, 2014

This of course places the EFF in a very interesting position. They've wanted to work with Numsa for a while but been snubbed. What now? — Verashni Pillay (@verashni) October 27, 2014

#Numsa Jim says Numsa wont allow anyone to seperate the union from the 2,2 million Cosatu members. — POWER987 News (@POWER987News) October 27, 2014

Is the breakaway from the alliance from Numsa significant? What does it even mean#Numsa — Jobe SC Sithole (@Jobza) October 27, 2014

#Numsa secretary general Irvin Jim just arrived. Briefing to start soon MV pic.twitter.com/2wPZC8CcHB — Jacaranda Newsteam (@JacaNews) October 27, 2014

Last week, labour columnist Terry Bell, wrote on Fin24 that trade unions both within Cosatu and among the other federations and independent organisations are being approached about the possibility of forming a single “super federation”.