More than 60 Labour peers have put their names to an advert in the Guardian accusing Jeremy Corbyn of failing to tackle anti-Semitism.
The signatories, who make up about a third of Labour members in the Lords, said the leader was presiding over a “toxic culture” of anti-Semitism.
Many of the 67 signatories are long-standing critics of Mr Corbyn.
A Labour spokesman said Mr Corbyn and the party stood “in solidarity with Jewish people”.
Labour has been engulfed in a long-running dispute over anti-Semitism, which has seen nine MPs and three peers leave the party.
Last week, the BBC’s Panorama revealed claims from a number of former party officials that some of Mr Corbyn’s closest allies tried to interfere in disciplinary processes involving allegations of anti-Semitism.
As well as calls for an investigation into the claims made in the programme, the Labour leadership is also under pressure to adopt an independent complaints process.
In the Guardian on Wednesday, the peers said Mr Corbyn had failed to accept responsibility for “allowing anti-Semitism to grow in our party”.
“The Labour Party welcomes everyone irrespective of race, creed, age, gender identity, or sexual orientation. Except, it seems, Jews,” the advert said.
“This is your legacy Mr Corbyn,” it added.
“Labour is no longer a safe place for all members and supporters,” it said.
It also accused Mr Corbyn of having “failed to defend our party’s anti-racist values”.
About a dozen of the signatories are former ministers who served in the last Labour government – including Peter Mandelson, Beverley Hughes and John Reid.
Those who signed make up about a third of the Labour members of the House of Lords.
A party spokesman told the BBC: “Regardless of false and misleading claims by those hostile to Jeremy Corbyn’s politics, Labour is taking decisive action against anti-Semitism.”
When the Panorama documentary aired, a Labour spokesman said the former employees who had talked to the BBC were “disaffected”, and included some officials “who have always opposed Jeremy Corbyn’s leadership”.
But more than 200 current and former staff wrote to Mr Corbyn to say the party had treated whistleblowers in an “appalling and hypocritical” way, and that the “moral responsibility” for the anti-Semitism crisis lay with the party’s leader.
Labour has never confirmed the number of anti-Semitism cases it is investigating and the scale of the issue among its supporters has become a source of political dispute itself.