NZME owns the NZ Herald, Herald on Sunday, nzherald.co.nz website, a range of regional newspapers, Newstalk ZB and entertainment radio stations, while Fairfax owns stuff.co.nz, the Sunday Star-Times and other metropolitan and regional newspapers.
A partner at law firm Simpson Grierson, Anne Callinan, said the draft decision raises questions about the extent to which the regulator can base its "decision on unquantifiable detriments to the public" and whether the commission had correctly assessed these.
"Obviously a draft determination that does not accept the authorisation is a significant setback, but it is not irreversible ... more often than not the commission has stuck to its draft determination, with one exception where it did change its mind from the draft decision and allowed the merger of two North Island ski fields," she said.
That case was the 2000 deal between Ruapehu Alpine Lifts and Turoa Ski Resort.
If the commission rejected the merger in its final decision, due on or before March 15, NZME or Fairfax could appeal to the High Court, Callinan said.
"A case of that complexity would likely take at least six months to be heard and decided," she said.
Both NZME and Fairfax have the next fornight to respond to the commission's draft decision and the regulator has also scheduled a conference next month where the parties can provide more information.
The two media companies made a joint statement to the New Zealand stock exchange yesterday, saying the commission's concerns relating to plurality of media were "unquantified".
"The parties' view is that the [commission] has failed to properly take into account the diversity of opinions that will continue post-transaction in an increasingly converged digital world," the two companies said.