DWYFOR Meirionnydd AM, Dafydd Elis-Thomas has been sacked by his party.
The move will see the AM lose his role as chairman of the Assembly's environment committee and his position as Plaid Cymru spokesman on transport.
Plaid Cymru acted after Mr Elis-Thomas criticised his leader's conference speech at the weekend.
In a statement Plaid Cymru's leader Leanne Wood has explained why she's taken action against Dafydd Elis-Thomas:
"Dafydd Elis-Thomas AM will be replaced as Plaid Cymru’s spokesperson on Transport and as Plaid Cymru’s nominee as Chair of the National Assembly’s Environment and Sustainability Committee.
"Plaid Cymru sought over the weekend to highlight the dangers posed to Wales by UKIP, because we fundamentally and sincerely believe that their politics and policies are not in the best interest of the people of our communities.
"Dafydd Elis-Thomas decided to publicly oppose this position without raising any concerns in advance.
"The people of Wales, and Plaid Cymru members, expect and deserve a national party that is united in addressing the challenges our country faces; on jobs, the economy and will continue to put Wales first.
"Alun Ffred Jones AM will be Plaid Cymru’s nominee for chair of the committee.
"He is a former Welsh Government Minister, and is an experienced and much respected colleague who has a keen interest in our nation's natural resources and in securing a sustainable and prosperous future for Wales.
"I am confident that fellow AMs will agree that he would be an asset to the committee as Chair. Rhun ap Iorwerth AM will be the Plaid Cymru Group Transport spokesperson."
Welsh Labour have criticised Leanne Wood's actions.
In a statement Welsh Labour said: “Plaid Cymru members might very well ask what is really going on here, and why it is that Dafydd Elis Thomas is continually slapped down by his party leader whilst others escape discipline. Despite repeated calls to do so, Leanne Wood refused to criticise Jonathan Edwards’ unacceptable comments about Wales captain, Sam Warburton. It seems that members of her senior leadership team get special treatment.
“Plaid Cymru are obviously incredibly rattled at the prospect of losing their seat in the European elections. But, everything they are doing at the moment – talking up UKIP as a threat, disciplining their most recognisable and popular AM and letting Mr Edwards run amok on twitter – this is all making Jill Evans’ defeat more, not less likely.”