The electricity and petrol hikes in April would be a harsh blow to the poor, Cosatu said on Monday.
"As might be expected, the poorest households, the least organised, worst resourced and most marginalised, who tend to vote for the ANC, bear a disproportionate burden," said Congress of SA Trade Unions spokesman Patrick Craven.
He said people were already battling to afford electricity and were constantly subjected to cut-offs.
"Despite progress in the provision of electricity infrastructure, a significant part of the population, 25 percent of households, are still without electricity at all and 53 percent of these use firewood for cooking."
Electricity is to increase by at least 16 percent in April, when the price of petrol will increase by 71 cents a litre in Gauteng.
Craven said even 25 percent of those with access to electricity used firewood for cooking, because of the cost.
"Cosatu has over and over again acknowledged and celebrated the tremendous strides made by the ANC government... [but] the current rates of unemployment, poverty and inequalities, and the unequal levels of service delivery, in particular as they affect women and youth, are a ticking time bomb," said Craven.