The Commerce Commission is investigating two models of ladder found to buckle under the maximum advertised load, and it's urging users to be careful.
The two models of Transforma ladder, which were sold nationwide between 2007 and March 2013, may be in breach of the Fair Trading Act.
About 16,000 of the ladders have been sold.
The commission's competition manager, Greg Allan said that both ladders had failed independent safety tests and there was potential for someone to be badly hurt.
People who bought the ladders have been contacted and other models of Transforma ladders were now being tested.
