The "multi-pronged offensive" to divide the Congress of South African Trade Unions is counter-revolutionary," the South African Communist Party (SACP) said on Tuesday.

"This is why as the SACP we strongly condemn all activities aimed at dividing and weakening Cosatu and our alliance," SACP general secretary Blade Nzimande said at a 20th anniversary commemoration of Joe Slovo's death, at the Avalon Cemetery in Soweto, according to a copy of his speech.

Slovo was SACP national chairperson, and an African National Congress national executive committee member. He served in the first democratic Cabinet as housing minister. He died on January 6, 1995.

Nzimande said the strategy to divide Cosatu, including attempts to separate it from the tripartite alliance with the SACP and African National Congress (ANC), represented a "classic imperialist strategy" to defeat revolutionary movements.

"In developing countries where there has been some relatively significant trade union movement, the imperialist strategy has been to drive a wedge between the national liberation movements and the trade union movement.

"This is what has been attempted in Zambia and Zimbabwe in our region."

He said the initiative led by the National Union of Metalworkers of South Africa (Numsa) fitted into the same imperialist strategy to try and dislodge the ANC-led alliance from power.

Numsa resolved at its special national congress in 2013 not to support the ANC or any political party in the 2014 national election and called for Cosatu to leave the alliance. It called for a united front that advocated for a workers' party.

Numsa was expelled from Cosatu in November.

Nzimande said there was already a "worrying phenomenon" negating trade union solidarity, replacing it with competition, and eroding the federation's unity.

He called on party members to honour Slovo's legacy by serving the people unconditionally.

"As South African communists let us honour comrade Joe Slovo by committing to serve our people without expecting any special favours for ourselves," he said.

"In honour of comrade Slovo, let all our ANC municipal councillors commit to serve and service our communities, and hold quarterly report back ward meetings in our communities."