Chairwoman Jane Diplock said the commission's 10th and latest surveillance cycle looking at the financial statements of 20 companies - a broad representation of issuers - had shown "a widespread lack of transparency".
The commission was "particularly concerned" about the lack of transparency around the underlying assumptions used to value assets, disclosures about transactions with related parties and the composition of unexplained expenses.
Ms Diplock warned directors "they could be failing in their duty to inform investors" by signing off financial statements that did not comply with New Zealand International Financial Reporting Standards (IFRS) which have been mandatory since 2007.
The commission said that "too often" the assumptions used to value assets were not sufficiently explained to allow investors to make informed judgements on whether the process was "fair".
The issue was particularly relevant given the global recession had prompted the need for such revaluations.
The commission had also sought explanations from six of the 20 companies after perceiving a lack of transparency in related party disclosure, "particularly where directors and other key management personnel are involved".
While the companies had been given the opportunity to provide explanations, Ms Diplock said, "if needs be, we'll take it to enforcement".
