The Democratic Alliance plans to march to Cosatu's headquarters in Johannesburg on Tuesday over job losses, spokeswoman Kelly Miller said.
"The march is to protest against the trade [union] federation's continued opposition to the youth wage subsidy, a policy that could create an estimated 423,000 jobs for young, unemployed South Africans," she said on Monday.
"In blocking this jobs initiative, Cosatu has become the key stumbling block to job creation."
DA leader Helen Zille, youth leader Makashule Gana, parliamentary leader Lindiwe Mazibuko and national spokesman Mmusi Maimane would lead the march.
It is scheduled to start on Beyers Naude Square at 10.45am.
Crowds would march along President street, Rissik street, Jeppe street, Sauer street, Melle street; Stiemens street, and Simmonds street.
It would end at Cosatu House on Jorissen street.
The National Union of Metalworkers of SA (Numsa) called on all workers to help it defend Cosatu against the DA.
"We welcome this class provocation and we will grab this opportunity to be frontal against white monopoly," it said in a joint statement on Sunday.
"We call on the workers and the youth to occupy the streets outside Cosatu House on Tuesday. We cannot allow the DA to mock us.... They now want to spit on the shield of the black and African working class."
It said the DA was a "representative of white monopoly capital and apartheid apologists".
On Tuesday, Numsa would be joined by the Progressive Youth Alliance, the African National Congress Youth League, the SA Students' Congress and the Young Communist League of SA.
"This DA march marks the beginnings of an open class warfare that will characterise the South African landscape," it said.
"We also view this open class warfare as a reflection of the deepening class antagonisms in our society."