"The memorandum dealt with a wide range of issues, the main one being that locals employed in the project are regarded as general workers," National Union of Metalworkers of SA regional secretary Jerry Morulane said.

"We are saying this cannot be allowed because they need to train and develop the workers. The workers need to continue with their lives beyond this project."

He said nearly 3000 workers participated in the march.

This number could not be immediately confirmed by police.

Morulane said the majority of workers involved in the construction of the station were employed by labour brokers -- as opposed to Eskom or its contractor, Murray and Roberts.

"We believe that this is slavery of the worst kind."

He said workers were also being harassed by a security company at the site that employed guards from the Democratic Republic of Congo.

"They intimidate our members. This is like something that happened in the apartheid era," Morulane said.