The Flag Referendums Bill sets out the process and questions for the two referendums, which are expected to cost $26 million.
The first will be later this year and ask voters to choose between four options for a new flag. The second will pit the most popular new flag design against the current flag and ask voters to pick one.
Labour has also said that voters should be asked whether they wanted to change the flag in the first referendum.
The flag designs for the first referendum will be decided on by a panel of 12 New Zealanders chaired by former deputy vice-chancellor of the University of Canterbury, Emeritus Professor John Burrows.
"The idea of two referendums is not common sense when $26 million would be better spent reinstating the Gisborne-Napier rail line, double lane-ing any number of one-way bridges in Northland or funding most of the first year of three-free GP visits for over 65s," Mr Peters said.
The RSA says it cannot afford to wait until after the centenary of Anzac Day this month to take its fight against proposed changes to the country's flag.
The New Zealand Flag Referendums Bill was introduced to Parliament last month and the closing date for submissions on proposals to the justice and electoral committee is Thursday, April 23.
RSA chief executive David Moger said the timing of the flag debate was insensitive.
"We feel it's inappropriate that these submissions close two days before April 25 when we will all be standing there as dawn breaks under the New Zealand Flag," Mr Moger said.
"We would prefer to allow the centenary to be commemorated without distraction but we have been forced to take action now because of the submissions date."
Time line
End of 2015
Referendum One: If the New Zealand flag changes, which flag would you prefer? (Voters rank four options in order of preference).
April 2016
Referendum Two: What is your choice for the New Zealand flag? (Voters choose between current flag and chosen new design).
