An ex-Welsh Government minister has quit the Labour Party and voted for the Greens, labelling his former party a "pro-Brexit anti-Semitic shambles".
Leighton Andrews was the Labour AM for Rhondda until he lost his seat to then Plaid leader Leanne Wood in 2016.
He said he had "loaned" his vote to the Green Party in the European elections because of the state Labour was in.
Mr Andrews is a supporter of a further EU referendum who has been critical of UK Labour leader Jeremy Corbyn.
He served as Wales' education minister and public services minister, but has been a vocal critic of Carwyn Jones's handling of the sacking of Carl Sargeant.
"In 2017 I voted Labour, and my vote has been waved around with that of millions of others as an endorsement of the leadership's plans for a better Brexit," Mr Andrews wrote on his blog, explaining why "I've loaned my vote to the Greens".
He added that he would like to rejoin the party, but warned if "Labour enables Brexit, I won't be back".
As well as accusing the Labour leadership of allowing the party to become a "pro-Brexit anti-Semitic shambles", Mr Andrews said "the far-right is on the march. Labour leadership could have pointed the way to a progressive alternative. Instead, it ducks the key decision of our time."
"When my postal ballot arrived two weeks ago, I returned it immediately with a cross against the Greens," Mr Andrews said, praising the work of Green Party MP Caroline Lucas and the party's MEP Molly Scott Cato.
Blaenau Gwent Labour AM Alun Davies echoed many of Mr Andrews's criticisms of the party leadership.
He told BBC Wales "principled leadership" had been "missing" from the party over the past three years.
"This is a time for principled leadership rooted in our values. That is the minimum our candidates, our members and our supporters deserved.
"And it has been missing in this campaign. We need to look hard at this campaign and think hard about where we've been over the last three years.
"The far right have been on the march and Labour has been a spectator."
Mr Davies added that he thought Mr Andrews's views "probably reflect the concerns and disappointment of most of our members".
Welsh Labour said they would not comment on individual membership, but said: "Our policy on Brexit - decided democratically at Labour conference - is to get a deal that protects jobs and the economy.
"If that cannot be secured and the Tories continue to dodge a general election, then the decision must go back to the people.
"Welsh Labour takes challenging anti-Semitism extremely seriously. As Mark Drakeford has repeatedly said, there is no place for anti-Semitism in the party and there is no place for anti-Semitism in Wales.
"We were delighted to welcome the Jewish Labour Movement to provide training on recognising and tackling anti-Semitism, for the second year in a row at Welsh Labour conference. We will do all we can to draw out the poison of anti-Semitism, wherever it exists."