Plaid Cymru AMs have unanimously voted to suspend Neil McEvoy from the party's group in the Welsh Assembly - the second time this year.
In an email to party members, leader Leanne Wood said he was "clearly breaching" Plaid's rulebook.
Mr McEvoy was recently accused by a Plaid colleague of undermining the party's policy on tenants' right to buy council houses.
He told BBC Wales he would continue to hold the government to account.
While suspended from his party's group, Mr McEvoy can continue to sit as an independent member of the assembly.
A Plaid source said Mr McEvoy's suspension from the Senedd group was independent of an ongoing internal inquiry into the South Wales Central AM's behaviour.
Under Plaid's standards of conduct, the party's AMs have to "accept a responsibility owed to the nation and the party to conduct themselves with due propriety and integrity at all times" and "must not act in such a way as to bring the group or the party into disrepute".
At Plaid's weekly group meeting in the Senedd on Tuesday morning, party AMs decided that Mr McEvoy had fallen short of those standards.
A party source said he "broke the trust" of the group in the way he had objected to a policy to stop the sale of council houses - a Welsh Government policy backed by Plaid Cymru.
Writing to members of the party after the decision, Ms Wood said: "His breach of numerous assembly group standing orders and our agreed code of conduct has caused distraction and disruption.
"As leader, I cannot allow elected members to act in a way which is detrimental to the party.
"We are a party and most importantly, a team. It is my duty not to allow behaviour which undermines its unity and integrity.
"I now look forward to the assembly group being able to move on strong and united, fully focused on the task of holding the Labour government to account and offering people effective representation at every level in all parts of Wales."
'Further bullying accusations'
Asked later by BBC Wales whether there was a way for Mr McEvoy to be admitted back into the group, Ms Wood said: "I don't know is the honest answer to that question.
"There have been a number of incidences over the summer talking about policy for example, attacking other members of the group and generally not treating other members with respect.
"Two members complained about that behaviour over the summer and the group collectively took action today."
Ms Wood added there were "a number of allegations that are with Plaid Cymru that are being investigated" against Mr McEvoy and these included "further bullying accusations".
In March Mr McEvoy was suspended amid a row over bullying but readmitted later in the month after issuing an apology.
He has the right to appeal against the latest decision to suspend him from the Plaid group.
It leaves Plaid Cymru with just 10 AMs, the smallest number since the assembly's creation in 1999.
Mr McEvoy told BBC Wales he was unable to comment on the suspension itself, but said it was "business as usual", saying he had been elected to hold the government to account and would continue to do so.
"My job is to ask difficult questions," he said.
"It upsets people sometimes, but that's why people vote for me."