Contact Energy says it has been told that Britain's BG Group has gained New Zealand overseas investment approval to buy Contact's Australian parent Origin Energy.
BG Group has launched a hostile bid for Origin, which owns about 51 percent of Contact.
BG has said that if it succeeds it would look to sell the Contact holding, which Origin bought from US firm Edison Mission in 2004.
Under New Zealand takeover law, if the owner of a dominant stake in a company changes, then a full takeover offer must be made to all shareholders.
The Takeovers Panel has said BG has a month from the time its Origin bid is unconditional to formally launch an offer for Contact, giving it the time to either find a buyer or offer its stake to the market.