New Zealand First MPs could face tough new rules and huge fines if they resign or are sacked from the party.
The rule - under which those MPs would be fined up to $300,000 if they didn't give up their seat within three days of leaving the party - was inserted into NZ First's constitution after Brendan Horan was ejected from the party in late 2012 but refused to resign from Parliament.
The rule is yet to be ratified.
Mr Horan was expelled from NZ First in December 2012 after his half-brother, Mana Ormsby, claimed he had inappropriately used their mother's bankcards.
However, the executor of his mother's estate investigated and cleared Mr Horan of any wrongdoing.
Legal experts said the new rules cannot be enforced and Mr Horan said the plan was undemocratic and a form of bullying. He told the Bay of Plenty Times the rule was "laughable", "completely against democracy", "a classic example of bullying tactics", and "a Winston decree".
"It's a classic grab for power and I feel sorry for the people who have supported NZ First."
Constitutional law expert Andrew Geddis, of Otago University, said the rule had no legal foundation, while public law expert Matthew Palmer said once an MP left a party he or she was no longer bound by its constitution.
However, NZ First leader Winston Peters disagreed. He believed the rule would be enforceable under contract law.
NZ First has tried to introduce a new "waka hopping" law via a member's bill.
However, Mr Peters said that attempt failed after other parties refused to support it.
The story so far
*Brendan Horan was expelled from NZ First in December 2012 after his half-brother, Mana Ormsby, claimed he had inappropriately used their mother's bankcards.
*The executor of his mother's estate investigated and cleared Mr Horan of any wrongdoing.
*Horan refused to resign from Parliament and is now an independent MP.
- Additional reporting Adam Bennett