Campaigners for MMP say there has to be strong democratic and natural justice principles at play for any MP who's expelled from their party.
There's debate around Parliament over whether the old waka jumping law should be resurrected.
It has been sparked by the Brendan Horan situation.
Spokeswoman Sandra Grey says there must be an open and sound process for expelling members of parliament.
"The things that we've been concerned about is that the processes the parties have put in place for choosing the lists, choosing electorate candidates, and then if they need to getting rid of them, must be a democratic process.
"It shouldn't be left to a single person and it shouldn't be behind closed doors."
Photo: Ed Swift