The Auckland-based Moana Pasifika bid and a Fiji-led delegation have been chosen to join the new-look competition in 2022, alongside the existing five teams from New Zealand and five from Australia.
But Kanaloa Pasifika have claimed NZR breached its own rules by appointing Moana Pasifika as a Primary Partner when the group did not take part in the formal tender process.
Kanaloa Chef Executive Officer Tracy Atiga said they have instructed their legal counsel to issue a letter to NZR today.
If the Union does not withdraw and retract its decision to appoint Moana Pasifika as the primary partner within 14 days, Kanaloa Pasifika Rugby will file proceedings with the high court seeking an injunction to the tender process.
New Zealand Rugby has been approached for comment.
Last week the Pacific Rugby Players Association welcomed the news that the region would finally have a team of its own in Super Rugby.
Chief Executive, Aayden Clarke, said while there was still details to work through, the Fiji and Moana Pasifika bids offered the best of both worlds.
"Having one there with Fiji, who've got a strong player base and very good high performance systems already set up.
"And if there's to be Moana Pasifika based out of initially New Zealand, which as you expect could possibly accommodate for a lot of Samoan and Tongan players, it's sort of two different systems being set up and being ready to go for 2022 but it's very much achievable and they'll be very strong teams."
Moana Pasifika is backed by a heavyweight group, including All Blacks legends Sir Bryan Williams and Sir Michael Jones, who are former and current members of the New Zealand Rugby Board.
However the overseas-based Pacific Rugby Players Welfare group expressed concern.
CEO and former Samoa international, Daniel Leo, said New Zealand Rugby needed to clarify how they came to their decision.
"As long as I've been involved with Pacific Island rugby the finger has constantly been pointed at the islands for their poor goverance, conflicts of interest involving officials, the lack of transparency and proper process and we've had funding frozen in the past due to those concerns."