The boss of Fairfax in New Zealand has stepped down.

Simon Tong has resigned just days before a Commerce Commission ruling on the proposed merger with NZME.

Tong, who joined Fairfax in September 2013, will leave next Friday and begin as ASB Bank's executive general manager technology, innovation and payments on March 27, making him part of ASB's executive leadership team.

Andrew Boyle will be acting Fairfax NZ managing director, the media company reported.

His exit comes as the Commerce Commission's decision on the media merger looms large on Wednesday.

The regulator released a draft determination in November rejecting the merger, saying it would "result in an unprecedented level of media concentration for a well-established liberal democracy" with the potential loss of multiple media voices a major part of the decision.

It was originally due last August, but was delayed due to the complexity of the deal.

ASB chief executive Barbara Chapman said Tong brings "a unique combination of skills, industry experience and knowledge to the role" and he has a "proven track record of managing large and dynamic organisations." Prior to Fairfax, Tong was chief executive of Paymark for seven years.

Tong said he was "thrilled to be joining the ASB team during such an exciting period of change for the financial services industry" and his background "provides me with a unique opportunity to contribute to the success of ASB."