Green Party MP Catherine Delahunty is unhappy she and party co-leader Metiria Turei have been told they cannot attend the Welfare Working Group's forum.
But, the group says the forum was never supposed to be a political forum and no other sitting MPs would attend.
Ms Delahunty said she, Mrs Turei and a staff member registered for the forum on May 19 and received confirmation emails.
Since then they were told their registration could no longer be accommodated.
Ms Delahunty said the forum was supposed to bring together diverse views and opinions.
"Of course the forum should maximise the participation of community and volunteer organisations, but this doesn't mean shutting out opposition MPs," she said.
The Greens would be happy to send along on representative to maximise space for community groups but "total exclusion at such late notice is unacceptable".
A spokeswoman for the Welfare Working Group said it was "unfortunate" the confirmation emails had been sent as the process was never meant to be a political one.
The group's recommendations would be presented to the Government and it would then enter the political process, she told NZPA.
The forum was an opportunity for the community and voluntary sector and business to "get together and engage independent of the political process".
The group had apologised to the Greens.
No other sitting MPs would attend the forum. Social Development Minister Paula Bennett would give a short welcome but would leave immediately afterwards and then discussions would begin, the spokeswoman said.
