Energy distributor National Grid reported a 21% increase in first-half pre-tax profits today and revealed that Superstorm Sandy on the US east coast will cost it around £100 million.
Pre-tax profits were £1.1 billion, with an operating profit of £1.59 billion, up by 7%.
A union representing workers at the company said the "bumper" profits came at a time when people were struggling to pay their bills.
The GMB also warned of possible industrial action over plans to transfer employees to contractors.
National Grid chief executive Steve Holliday said: "I am pleased with the progress we made in the first half of the year - operating our networks safely and reliably and delivering a record level of investment.
"More recently, our teams in the US responded in a timely, safe and effective way to restore service to our customers and limit disruption caused by Superstorm Sandy.
"This good first half-year performance reflects increased net regulated revenues driven by our growing asset base and tight control over operating cost growth. Increased investment in both our UK and US operations is in line with our forecast."
National Grid said it had made improvements to the way it responded to storms in the US, adding that its teams restored power to around 400,000 customers on the east coast affected by the latest superstorm within three days.
The organisation said it had increased capital investment by 23% to £1.8 billion in the latest period, mainly due to a 34% rise in investment in its UK transmission business.
Gary Smith, national officer of the GMB, said: "People are entitled to ask what is National Grid putting back when they have outsourced and plan to outsource more and more jobs.
"Hundreds of National Grid staff are facing being transferred out to contractors. This has implications for the pay, conditions and pensions of loyal National Grid employees, many who have given decades of dedicated service.
"GMB members want to take action and we are encouraging other unions to join us in a campaign up to and including industrial action to stop this shameful attack."