The energy watchdog is to look into claims networks are charging vastly different prices to customers for some routine jobs.
Small-scale work like moving an electricity meter can range from a few hundred pounds to more than £5,000, depending on which network carries it out, according to an investigation by The Times.
Installing or moving meters are considered small-scale jobs and networks should not make a profit from such work, the regulator Ofgem said.
For bigger jobs like connecting to a new supply Ofgem said it encourages competition to offer customers "real choice".
The Times said it found the cost of a new electricity supply ranged from £840 to almost £3,000 in different areas.
It also claimed the difference between networks in providing a new gas supply could be as much as 400%.
A spokeswoman for Ofgem confirmed it would "ask network companies to explain the differences highlighted by the investigation".
She added that customers should challenge firms if they think they are being overcharged.
"Consumers should always be provided with a quote before having a job done, and if they feel they are being overcharged we would encourage them to challenge the network companies.
"If their issue is not resolved within eight weeks, they may be able to refer the complaint to the Ombudsman and ultimately customers can bring disputes to Ofgem so that we can investigate the cost and see if they're justified."