Two major power and utility companies are being put on notice, over leaving out GST from their prices

The Commerce Commission says Contact and Nova are being "unhelpful" - by not giving consumers the full price.

The competition watchdog says it will take "other action" if they don't change their practices.

Mercury, Electric Kiwi, Pulse Energy and 2degrees have already done so.

Meanwhile, the Electricity Authority has confirmed new "obligations" for power companies, taking effect from next month.

All fees and charges will need to be "reasonable' and retailers won't be able disconnect customers known to be medically dependent.