The chairman of the Energy and Climate Change Select Committee has said it is unfair that online customers get the best gas and electricity deals.
Customers on standard price plans are said to pay on average almost £140 a year more than those on online plans.
MP Tim Yeo told BBC Radio 4's Money Box that the elderly and the vulnerable, who may not use the internet, should still have access to the best deals.
Industry body Energy UK said discounted "social tariffs" were available.
A recent survey of the big six suppliers by online comparison site uSwitch revealed consumers could save more than 10% on their gas and electricity bills if they signed up for online tariffs.
In one scenario someone paying by cheque or cash on a standard tariff could pay £400 more a year than someone paying for an online tariff by direct debit.
"The tragedy is that the very group that we most want to reach to give them the best chance of switching to the lowest tariff includes a large number of people who simply don't have access to the internet," Mr Yeo said.
"I do think it's time the companies faced up to the fact that the only way to be fair to this particular group is to offer them access to the same tariffs."
Lucy McLynn, a discrimination law expert, told Money Box there may be grounds for a legal challenge.
"In the future there may well be the potential for an individual to challenge retailers who sell their goods more cheaply online," she said.
"The prohibition on discrimination on the grounds of age in the provision of goods and services will be brought in from 2012. Issues of 'web discrimination' are and have already been at the forefront with regard to disability discrimination,"
Currently the 2010 Equality Act does cover age discrimination but it does not extend to goods and services.
In a statement Energy UK said: "Elderly and vulnerable customers in particular may be eligible for social tariffs, which provide special low prices to people struggling to pay their bills."
Watchdog Ofgem said that there were currently no licence obligations on energy suppliers to offer social tariffs "although many of them follow a voluntary agreement, which is at the discretion of the supplier".