Credit ratings agency Standard & Poor's has kept Telecom NZ (ASX:TEL) on its CreditWatch list for a possible downgrade, due to the implications of the Chorus demerger.
The agency on Tuesday maintained Telecom NZ's long-term and short-term ratings at A and A-1, respectively.
But it added that a Chorus demerger would "likely result, all things being equal, in a lowering of the long-term rating ... by at least one notch".
Telecom NZ gained its existing ratings due to its position as New Zealand's incumbent telecom service provider, S&P's said.
But structural separation, as well as the threat of increased regulatory restraints and competition, would challenge this position.
But the agency added that a rating outcome of A- would be possible for the group if it maintains a conservative capital structure and financial policies post-demerger.
Its strategy regarding its remaining business in Australia as well as its ICT operations could also influence its long-term rating.
Telecom NZ agreed to split off its Chorus network division as part of its participation in the government's Ultrafast Broadband fibre project.
Last week, Telecom NZ booked a 56.8 per cent decrease in reported FY11 profit, due to costs including a writedown on the value of its soon to be largely obsolete copper network.
TEL shares fell 0.93 per cent in Tuesday's trading to $2.140.
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