Sir Michael Cullen had been paid more than $84,000 for his part time role as head of the Tax Working Group, even before the Government revealed his term had been quietly extended.
In an answer to a Parliamentary Question, Finance Minister Grant Robertson revealed that by March 6, a day after Cullen's ongoing role as Tax Working Group chairman emerged, the former Labour MP had been paid $84,115.05.
The answer added that some of the invoices for the period had not been covered.
The figure for the part-time role is more than twice the amount a worker on the new higher minimum wage working a 40-hour week would earn in a year. Based on Cullen's daily rate of slightly more than $1000 for a six hour day, National says the pay amounts to less than four months work.
In total, the 11 members of the working group members had been paid just over $425,000, Robertson said.
The group's report recommended a broad-based capital gains tax, although three of the group's members declined to support the findings.
Currently Labour and its support parties are negotiating what to do with the report.
Revenue Minister Stuart Nash told a tax conference in Queenstown in March that the Government would publish its response to the report "in early April".
Several weeks after the report was released, Treasury officials sent out a a press release from Cullen, criticising arguments used by National Party leader Simon Bridges.
The day after the release was sent out, Robertson confirmed that Cullen's extension had been extended, meaning he would continue to be paid up to $1062 a day, although after news broke Cullen played down how many days he would charge in the ongoing role.
National has said the Cullen appointment is political, with the former minister being used to defend the proposals against Labour's political opponents.
A nine-term Labour MP and long time finance spokesman, Cullen spent nine years as Minister of Finance, from 1999 to 2008.
"Since the Tax Working Group's final report was published in February, Sir Michael has been kept on his retainer to defend the proposed capital gains tax from criticism," National finance spokesman Amy Adams said.
"As a result, we're in the bizarre situation of having a former Labour Finance Minister being paid by the taxpayer to stop people criticising plans to add more taxes."
Adams said the nature of Cullen's pay meant the amount "covers less than four months of actual work".
Meanwhile Employment Minister Willie Jackson said in Parliament that Cullen was "doing us a favour" because lawyers working for the Government were charging far more.
A spokesman for Robertson said Cullen was being paid according to Cabinet guidelines.
Almost a month after Cullen's contract extension came to light, a spokesman for Prime Minister Jacinda Ardern has not responded to questions about whether other working group chairs or members have had their contracts extended in the way Cullen's was.