PLAID Cymru big hitter Dafydd Wigley last night rounded on Ukip, branding it a destabilising force.
The former party president called on voters to protect what was good about Europe ahead of the forthcoming European elections.
He described the threat of pulling out of the EU as a course of action that would have disastrous and destabilising consequences for Wales and the nation's economy.
"For Ukip, the point of holding a referendum is to pull the countries of Britain out of the EU," he said in Merthyr. "So I understand why those who want to turn their backs on Europe should want a referendum. I don't want Wales, or Britain, to pull out of the EU."
And he warned Welsh voters against channelling any frustrations about aspects of European policy by voting Ukip.
"Ukip is a single issue party, whose answer to every question is to press the self-destruct button on European unity and co-operation," he said.