The United States has classed the Hector dolphin as threatened and Māui dolphin as endangered - despite the species living in New Zealand waters outside US jurisdiction.
The US has previously called for more to be done to protect the dolphins, endemic to New Zealand.
Last year, the US National Marine Fisheries Service said listing the species could help conservation efforts and, at the time, an Otago University zoologist said it was embarrassing for the New Zealand government.
Māui - popoto - and Hector's dolphins, with their rounded black dorsal fins, differ from other members of the 32-species mammalian family. Māui and Hector's dolphins appear identical, but they are genetically and physically different - Māui dolphins have larger skulls and longer, wider snouts.
Hector's dolphins are most commonly sighted off the South Island coast and Maui's dolphins along the west coast of the North Island. Their range is limited to coastal New Zealand.
Commercial fishing bycatching - especially from gillnets - has caused dramatic population decline.
The population of Hector's dolphins is estimated at 9000. Māui dolphins number at 50 to 60 individuals.
Federal US agencies, the National Oceanic and Atmospheric Administration and the National Marine Fisheries Service, listed the dolphins as endangered and threatened on Monday.
In its ruling, the NOAA said the agency determined the dolphins warranted listing.
"We will not designate critical habitat for either of these dolphin subspecies, because the geographical areas occupied by these dolphins are entirely outside US jurisdiction, and we have not identified any unoccupied areas within US jurisdiction that are currently essential to the conservation of either of these subspecies."
Internationally, both species are listed as being under threat of extinction.