Responding to Dafydd Elis-Thomas's decision to leave the Plaid Cymru Assembly Group, a spokesperson for the party's Dwyfor Meirionnydd constituency committee said:
"We thank Dafydd Elis-Thomas for his work for the party and the constituency since 1974.
"We are saddened and disappointed by his departure.
"The local constituency committee now appeals to his conscience and requests that he stands down in order to allow for a by-election.
"We will be making no further statements at present."
A Plaid Cymru party spokesperson said:
"Plaid Cymru will begin the process of selecting a new candidate in Dwyfor Meirionnydd following Dafydd Elis-Thomas's decision to leave the Plaid Cymru Assembly Group.
"Constituents, who Dafydd Elis-Thomas misled in the recent Assembly election, will expect a by-election to be held at the earliest convenience."