Energy watchdog Ofgem has launched an investigation into supplier 'E' following concerns over the company's sales practices.
The Birmingham-based firm, which has 200,000 customers predominantly on prepayment meters, is being investigated over the marketing and sales practices it uses to recruit new customers.
It's suspected that E may have broken rules requiring energy suppliers to provide customers with accurate and transparent information when promoting products.
An Ofgem spokesperson says: "We are currently looking to see whether the company's sales and marketing has misled customers, and whether the company has communicated fairly and with transparency.
"However, the fact that the investigation has just launched does not mean that we have found any problems with non-compliance."
E declined to comment when contacted by MoneySavingExpert.com.
Increased Ofgem action amid marketing concerns
This is the second time in as many weeks that the energy regulator has launched an investigation into concerns around marketing and sales practices.
Coventry-based Economy Energy is currently being investigated by Ofgem amid fears its marketing and telesales practices could have broken the rules.
Like E, Economy Energy mainly supplies gas and electricity to households with prepayment meters.
Ofgem said it would focus on "concerns" about how the supplier recruits new customers as its behaviour may have breached licence conditions to communicate "transparently and accurately" with customers.
An Economy Energy spokesperson says: "We are co-operating fully with Ofgem and customer satisfaction remains our utmost priority at all times."
If you think you've been incorrectly billed or mis-sold an energy contract, check out our Energy Complaints guide for help on getting it sorted.