It is regrettable that Cosatu was left with no option but to expel Numsa, the South African Communist Party's political bureau said on Tuesday.

"For many months, throwing reckless insults in all directions, the Numsa leadership has shown no inclination to seek constructive and unifying solutions to the many challenges confronting the organised working class," SACP spokesperson Alex Mashilo said in a statement.

"This was not a case of an externally manipulated witch-hunt, but a case of self-expulsion."

The SACP called on members of the National Union of Metalworkers of South Africa (Numsa) not to follow the union's leadership and to remain where they could help re-build unity in the Congress of South African Trade Unions (Cosatu).

Numsa was expelled from Cosatu during a special central executive committee meeting which ran into the early hours of Saturday morning.

During the meeting Numsa presented its argument to Cosatu on why it should not be expelled, but this did not stop its ousting by 33 votes to 24.

Numsa has been at loggerheads with Cosatu since its general secretary Zwelinzima Vavi was suspended last year for having an affair with a junior employee.

She originally claimed he had raped her but did not press charges with the police. Numsa took Cosatu to court to reverse the suspension, where it won its bid and Vavi returned to work.

Numsa held a special national congress in December where it resolved not to support its traditional ally the ANC in the general elections.

Cosatu charged Numsa with contravening its constitution.