Energy customers should not be seen as "cash cows", to be "squeezed" in the pursuit of a higher return for shareholders, Ed Davey will say tomorrow.
The Energy Secretary is expected to tell Energy UK's annual conference that trust between firms and customers was breaking down, amid continued controversy over soaring bills.
Power companies have to make profits so they could invest in energy infrastructure, secure supplies and develop more energy efficient technologies, as well as create jobs, he will tell the London conference.
"But those profits cannot come at the expense of the elderly, the vulnerable, and the poorest in our society," Mr Davey is expected to say.
"Customers are not just cash cows to be squeezed in the pursuit of a higher return for shareholders".
Energy firms criticised for 'losing public trust'
Energy Secretary Ed Davey is walking an uncomfortable line by hitting out at the same firms he needs to improve our energy infrastructure.