ScottishPower put up gas prices by almost 20% and electricity by 10% yesterday, adding hundreds of pounds to the average annual household energy bill from August this year, with other firms expected to follow suit.
John Robertson, Glasgow North West Labour MP, has called on Chancellor George Osborne to take action and to rethink his cut in the winter fuel allowance this year.
Mr Robertson, a member of the Energy and Climate Change Select Committee, said pensioners would be hardest hit as they will lose up to £100 this winter just as the increased bills start to be delivered.
He said most of those aged 60-79 will get £200 instead of last year's £250 when the payment is made in November or December. Those who are 80 or older will get £300 instead of £400.
He said "People in Glasgow and the rest of Scotland are struggling to keep warm at winter, and the big energy companies are mugging the poorest people in our country.
"The big six energy companies are acting like a cartel and instead of price rises being the last alternative it seems to be the first. They seem to view consumers as cash cows and the Chancellor seems to view the poorest consumers with contempt.
"These companies are pinching money out of the pockets of the poorest people in this country at a time when ordinary household budgets are threadbare."
Housing charity Shelter Scotland said the rise would put even more families into poverty.
Gordon MacRae, head of policy, said: "Prices cannot keep going up – something's got to give. Either the short-term profit margins of utility companies or, for families, the choice of heating or eating. We fear that more families will not be able to pay their bills and eventually lose the fight to keep a roof over their head."
The SNP also condemned the price rise. Energy spokesman Mike Weir MP said: "People just cannot keep absorbing continuous and colossal energy price increases like this, and the UK Government must step in."
ScottishPower said the rise was necessary due to increasing cost of wholesale prices.
Raymond Jack, ScottishPower's UK Retail director, said: "Wholesale prices for gas and electricity have increased significantly since the end of last year and continuing unrest in global energy markets means future prices are volatile.
"We understand times are difficult for many people, and we have done what we can to absorb these additional costs for as long as possible to minimise the impact on our customers."