Aberporth county councillor Gethin James has been asked to leave his seat on Ceredigion's Cabinet after announcing he had joined the UK Independence Party.
Council leader Cllr Ellen ap Gwynn said that UKIP policies had nothing in common with the county's Plaid/Indpendent coalition.
"I have given Cllr James the formal statutory two days notice," she told today's Cabinet meeting.
Cllr James, who held the planning portfolio, attended the meeting but sat with backbench councillors.
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