Click Energy is putting its electricity prices up by 11% from the start of July.
The company is the smallest of Northern Ireland's five energy suppliers and the move will impact around 26,000 customers.
It means the typical household bill will go up by almost £100 per year, according to the Consumer Council.
Raymond Gormley from the organisation says the increase is "due to the continuing rise of wholesale energy costs".
He said it comes at a time when "many are already experiencing extreme pressures on their household budgets".
A number of other companies including Power NI, SSE Airtricity, Electric Ireland and Budget Energy have also raised their prices in recent weeks.