Firmus gas customers in the Greater Belfast area are to face a massive 35.4% hike in their gas bills in the latest blow to beleaguered consumers.
The price rise affects 9,000 customers in Belfast and nine other towns in the surrounding area and comes into force from October 1.
It follows a 28.4% hike in Firmus's prices for the other 10 towns in which it operates earlier this month and is said to be the result of a surge in the wholesale price of gas.
John French, head of energy at the Consumer Council, said: "This is further bad news for consumers in a year that has seen other large price increases in electricity, home heating oil, gas and coal - especially given that Northern Ireland has higher energy bills than England, Scotland and Wales."
Despite the price rise, Firmus said it would charge its customers in the Greater Belfast area 10% less than its rival Phoenix, more than the 7.5% discount it originally promised to customers that switched.
The company claims it offers credit meter consumers the opportunity to make a saving of £200 on the cost of gas in two years.
Firmus energy spokesman Michael Scott said: "The good news for the 8,500 customers who have switched online or on the phone to Firmus Energy is that we have not just honoured our guarantee to be cheaper but have increased our discount to 10% less than Phoenix for the first year."
But Ulster Unionist MLA Mike Nesbitt said Firmus had not been transparent about the price increase, after the company told news organisations yesterday that it was continuing to keep its prices below those of Phoenix without mentioning the price hike.
Yesterday Phoenix Supply said it was holding prices for around 130,000 natural gas customers in Greater Belfast.
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Consumers have been hit by a series of crippling rises to energy prices. Phoenix Supply prices went up by 39.1% in May. Last month Power NI - the new name for NIE Energy - said its prices were rising by 18.6%. Other towns that come under Firmus's Greater Belfast region include Bangor, Castlereagh, Carrickfergus, Holywood, Larne and Lisburn.