Poor households will be hardest hit by yet another increase in the price of fuel, the Congress of South African Trade Unions (Cosatu) said on Tuesday.

The energy department said at the weekend the price of petrol would go up by up to 26 cents per litre from Wednesday, citing a weaker rand against the dollar. This follows another steep increase last month.

Cosatu spokesperson Sizwe Pamla said the labour federation was "deeply alarmed" by the escalating price of fuel.

"This spells bad news for all South Africans but the impact on poor families will be even worse. This increase in fuel prices will create a level of hardship for a group that is already suffering from high levels of unemployment and stagnant or declining real wages," he said.

"Low- and moderate-income families are going to plunge further and further into debt because their wages are now inadequate to afford the basic amenities."

The energy department said diesel prices would rise by 24 to 26 cents a litre while the wholesale price of illuminating paraffin, used by many households that cannot afford electricity, would increase by 22 cents a litre.

The single maximum national retail price was set to go up by 30 cents, while the maximum retail price for LP gas would increase by 37 cents per kg.

Pamla said the increase in the price of paraffin would leave many poor families worse off.

"The chilly winter conditions will force many poor families to resort to dirty energy like coal, leaving them vulnerable to health hazards," he said.