By RNZ
The Commerce Commission wants a "please explain" after timber giant Carter Holt Harvey abruptly cut supplies to a number of building retail chains, prompting concerns that costs will rise and construction could slow.
The company has stopped selling structural timber to ITM and Mitre 10 but continues to supply to some of the bigger operators.
The Commission says it was aware of supply issues in the building industry, however Carter Holt had not specifically advised the commission of its intention to cease supply to some customers. And it says it will speak to Carter Holt to understand what is happening and the potential ongoing implications for competition.