Waikato-Tainui and Ngai Tahu have received top-ups on their Treaty of Waitangi settlements reaching $370 million, the Government has confirmed.
The payouts, made in December, saw Ngai Tahu receive $180 million and Waikato-Tainui $190 million, according to Fairfax.
The top-up was triggered by an old "relativity clause" in the original 1994 treaty contracts which said once total iwi settlements reached $1 billion, both tribes would be entitled to a percentage of all future settlements.
Ngai Tahu would be entitled to 16.1 per cent and Waikato-Tainui to 17 per cent of all future settlements to other iwi, in 1994 dollars.
December's respective payouts are more than either iwi originally received.
The clause had previously been triggered in 2013 when Ngai Tuhoe settled its claim, tipping total claims over the $1 billion threshold.
At the time National's treaty minister Chris Finlayson said that in 2017 the two iwi would be able to seek a further payment related to settlements reached in the intervening five-year period.
The clause was negotiated in order to ensure the two iwi retained their position in relation to other iwi groups. Other iwis' settlements do not include relativity clauses.
Ngai Tahu had not told its 58,000 iwi members about the latest payout, according to Fairfax.
Taxpayer's Union director Jordan Williams told NZME it would have been impossible for the Government to avoid the payouts, thanks to the relativity clauses.
But he raised concerns about the "secretive" way the payments had been made - and the fact that iwi leaders did not appear to have informed their members.
"The relativity clauses are no secret - I think that what many NZers would be concerned about is the way that this payment has been made. It was done behind closed doors, we've only discovered months later.
"It seems a little bit secretive to make hundreds of millions of dollars of these payments without being totally transparent with the taxpayers paying for it."