Firmus Energy has announced a further gas price hike of 56.3% for its Northern Ireland customers.
The increase, which will impact customers in the Greater Belfast and Ten Towns network areas, will take effect from 3 October.
It is the largest in a series of energy price rises announced by companies in Northern Ireland in recent months.
Sinn Féin vice president Michelle O'Neill said the increase was "staggering and catastrophic". She said it underlined the need for an Executive to be formed at Stormont.
Ms O'Neill said: "News that Firmus are increasing gas prices by a staggering and catastrophic 56.3% is yet another crushing blow for workers and families who are really struggling to pay their bills.
"Their average annual bill will have risen by over £1,500 in the space of a year, that scale of increase is devastating.
"They have had enough. They need help now. They need an Executive up and running and working to put money in their pockets."
The North's Consumer Council described the price increase as "shocking" and warned that customers are facing a crisis this winter.
Firmus Energy said continuing increases in global wholesale gas prices are impacting the tariffs of local energy suppliers.
Niall Martindale, the company's chief executive, said: "Increases in wholesale gas commodity costs continue to impact the market and, regrettably, we have no choice but to reflect these increases in our tariffs.
"The ongoing war in Ukraine and Russian disruption to the supply of natural gas in Europe is having a significant and adverse impact on energy costs, affecting all suppliers here in Northern Ireland, as well as nationally and internationally.
"We know this is not welcome news.
"Tariffs are set as a direct consequence of wholesale prices on the global market and we have no option but to reflect the cost of this gas within our tariffs.
"We remain committed to reducing tariffs as soon as the market crisis subsides and enables us to do so."
