Environmental campaigners are calling on McDonald's to stop sourcing fish caught in New Zealand waters, and for Filet-O-Fish fans to try something else on the menu.
Leaked Ministry for Primary Industries documents and an international study have revealed huge amounts of fish are being dumped and under-reported.
McDonald's sources 8 percent of its fish from New Zealand, because hoki fishing here has been certified sustainable by the Marine Stewardship Council (MSC).
"We understand the importance of protecting marine wildlife, especially endangered species that share the ocean with the fish we use on our menu," McDonald's told the BBC.
"The New Zealand hoki fishery is considered one of the most well-maintained and controlled fisheries in the world, and was one of the first fisheries in the world to be awarded MSC certification for sustainable fishing."
Campaigners say they're not attacking McDonald's, but giving the global food giant a chance to "bring about some real change in the New Zealand Government and fishing industry".
"They could say they saved the Maui's dolphins, and how good would that be for their brand?" says Dr Barbara Maas, from dolphin protection lobby group Nabu International.
The leaked documents show the endangered dolphins are sometimes caught in fishing nets, but aren't always reported.
Primary Industries Minister Nathan Guy and MPI deputy director-general Scott Gallacher have both denied accusations of a cover-up, the latter saying the leaked reports were "internal, draft investigations" only leaked in part.
LegeSea, which represents fishing clubs around New Zealand, says Mr Guy has been caught napping.
"He's been largely absent this last week and it's his ministry. They're very definitely under siege and we do not believe that they should be organising this independent review," says Richard Baker.
Mr Baker says MPI can't be trusted to set the boundaries of the review and that Mr Guy has been in damage control all week.
"It's a credibility issue; there has been a huge amount of credibility lost over the last week."