"The court found that our application meets the standard for urgency and therefore granted us the interdict", Numsa said in an emailed statement.
"There is no evidence at this point that these independent renewable energy providers will be able to retain the same number of workers now employed in the coal fired power stations".
The order is another setback for energy developers including Denham Capital-backed BioTherm Energy and ACWA Power International that have been waiting for deals to be signed since 2016.
Minister Radebe was due to hold a signing ceremony for bid Window 3.5 and Bid Window 4 of the Department of Energy's Renewable Energy Independent Power Producer Procurement (REIPPP) Programme at the department's Independent Power Producers (IPPs) office in Centurion, Tshwane, on Tuesday morning.
The signing was postponed at the 11th hour following a court application to be considered in two weeks' time.
This after trade union National Union of Metalworkers of SA (Numsa) and civic group Transform RSA were granted an urgent court interdict at the North Gauteng High Court.
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Numsa said the signing of these contracts "would be detrimental for the working class of Mpumalanga and the country as a whole".
"The signing of the IPP means Eskom will require less coal-fired electricity".
Meanwhile the minister maintains that the signing of the 27 projects will contribute significantly to job creation across the value chain including the reestablishment of industrial development and support to the technical training of young people to be absorbed in the labour market. It claims that the signing of PPAs for renewable energy would likely result in the closure of coal-fired power plants, which in turn would affect 30,000 working class families.
The High Court is set to hear the case on March 27, the interdict has stopped Radebe from signing the contracts until the case brought by Numsa and Transform SA is heard. The country's power mix has always been dominated by coal.
Coal ash disposals in South Africa.
He added that the department will continue to defend the right of consumers to have access to cost efficient clean energy that will bring much needed investment in South Africa, as well as jobs and small business entrepreneurial opportunities in rural communities.