Plaid Cymru has been appalling at dealing with disciplinary issues, according to one of the party's own AMs.
Simon Thomas criticised a disciplinary process against Neil McEvoy in the party that has "dragged on" for months.
He, and the rest of Plaid Cymru's AMs, have decided to expel Mr McEvoy from its assembly group, alleging a breach of trust.
Mr McEvoy said there had been a "concerted campaign" to undermine him.
Separate from his expulsion from the Senedd group, the South Wales Central AM and Cardiff councillor is facing a party investigation into allegations about his behaviour.
Referring to the internal party process, which was announced last March, Mr Thomas said: "I think Plaid Cymru has been appalling with dealing with disciplinary issues.
"I think one issue that both myself and Neil McEvoy would agree upon is that this disciplinary process outside the group has dragged on for months without resolution.
"Neither of us would be happy about that.
"I would challenge the party more widely to look at disciplinary processes and to ensure that people selected as Plaid Cymru candidates do what they are signed up to do."
On Tuesday Mr McEvoy was told by the party's AMs that they no longer wanted to work with him, citing "inaccurate" claims Mr McEvoy made about his suspension and others in the group.
Speaking to BBC Radio Wales, Mr Thomas said: "We feel Neil McEvoy's way of working has undermined fellow assembly members, has left us demoralised and talking in every group about his behaviour."
"We simply have found ourselves in a position where the trust has broken down", Mr Thomas told the Good Morning Wales programme.
Mr Thomas also said Mr McEvoy had used "a legal access order to demand information".
"He's perfectly at liberty to do so - it's his legal right - but it doesn't demonstrate to us a person wishing to work with us in the future," he said.
'Smear after smear'
Mr McEvoy said he did not see where the Plaid AMs were coming from.
"What has been happening over the last 18 months has been a concerted campaign to undermine me," he said.
Mr McEvoy said: "Since March last year I have had to deal with allegation after allegation, smear after smear, of generality really - just general attacks.
"What I really want - and what members of Plaid Cymru want - is some specifics.
"What I should be allowed to do is get on with the job of holding this Labour government to account."
Plaid Cymru has passed complaints from the internal party inquiry into Mr McEvoy to the assembly's standards commissioner, although one source told BBC Wales that not all of the complaints had been handed over.
Neil McEvoy has now written to the commissioner asking him to investigate complaints against him.
The South Wales Central AM is asking the commissioner to waive a rule which means he cannot investigate complaints that are more than a year old.
In a letter to Mr McEvoy, Sir Roderick Evans QC says he is yet to decide if he is going to investigate.
Mr McEvoy was under his second suspension in a year when he was expelled from the Senedd group.
Despite being reinstated for a few months, Mr McEvoy was suspended again in September 2017 after a public row over his opposition to Plaid Cymru's support for a ban on people's right to buy council houses.
Mr McEvoy was accused of breaching a code of conduct, with AMs said to have been unhappy with how the AM went about expressing his views.
In an email sent to a party member who complained about the second suspension, Plaid Cymru leader Leanne Wood said Mr McEvoy was "impossible to work with".
His expulsion means that Mr McEvoy remains an independent AM in the eyes of the assembly authorities, as he had during his suspension.