Npower is to be probed by industry watchdog Ofgem over claims that it has been mis-selling energy contracts to customers.
The investigation follows reports in the media that some of the company's sales representatives have misled members of the public with the aim of getting them to switch their energy supply to npower. The energy firm, one of the UK's big six providers, has already suspended 17 members of its sales force and more action has been signalled.
"We were very concerned at the actions of a small number of individuals in a London sales team, as reported," said an npower spokesperson.
"We took swift action to take the team off the road and investigate the problem. Following an in-depth investigation by our audit team, disciplinary hearings will be scheduled shortly."
The company has embarked on a retraining scheme and said that it would start a "mystery shopping" programme to monitor its sales team.
Instances of mis-selling have been common in the highly competitive energy market. However, it had been thought that matters had improved recently. If the Ofgem investigation, which is expected to take several months, finds that npower is at fault, the company could be fined up to 10 per cent of turnover.