Labour leader Andrew Little will try to call the Prime Minister's bluff by trying to introduce a bill to include Red Peak - but also change the order of the flag referendums' questions.
His move comes after Prime Minister John Key said he would consider including Red Peak if other parties in Parliament agreed - especially Labour.
Labour had criticised the flag change process from the outset, arguing it cost too much and that the first referendum should ask whether people wanted to change rather than waiting until the second.
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Mr Little responded to Mr Key's challenge by saying Labour would support it, but only if the change question was included in the first referendum.
This week he will try to table a bill which does both - although that can be voted down if just one MP objects.
It would mean the first referendum would allow voters to rank their favourite alternatives as well as vote on whether they wanted change. If a majority wanted change, a second referendum would pit the current flag against the alternative. If the majority wanted to keep the current flag, there would be no second referendum.
Mr Little has previously said he will not vote in the referendums by way of protest, although he supports a flag change and it was long-standing Labour policy.
"Labour has disagreed with the timing of the flag change and the process was botched from the beginning, but there is still time to make this right."
He said putting the change question first gave everyone something to vote for because it effectively allowed them to choose the current flag in the first referendum.