Two of the major international ratings agencies have put Chorus' credit rating on review for a possible downgrade.
Standard & Poor's currently rates the company's debt at its investment grade BBB and Moody's at its equivalent Baa2 rating.
Both agencies say their reviews have been prompted by Tuesday's ruling by the Commerce Commission that the price Chorus can charge for broadband over copper wires must nearly halve by December next year.
The decision means the total price Chorus can charge for its copper wire broadband and phone services will reduce by about $10 a month to $34.44 in December next year.
Chorus has already said the decision, if allowed to stand, would cost it about $1 billion by 2020.
S&P credit analyst Paul Draffin says if the commission's ruling is allowed to stand, Chorus will probably breach covenants under its debt facilities from 2015.
"Our forecasts indicate that if the determination is allowed to proceed without amendment the company will fall outside expectations for the current rating but more importantly it will also breach covenant under its bank facilities."
Mr Draffin says one of the reasons that S&P has put the rating on credit watch rather than downgrade it straight away is that there may be ameliorating circumstances which evolve over the next few months and an important part of that is the Government's telecommunications review outcomes.
