Jewish groups protesting against anti-semitism in the Labour party last year.
Some 128 of them - more than two-thirds of the total - signed a letter of support to the Jewish Labour Movement.
The organisation, which is Labour's longest-standing affiliate, will vote next month on whether to sever its ties with the party.
That follows concerns about the way Labour has tackled the anti-semitism rows which have dogged it in recent years.
In the letter, which was sent last Friday, the peers said: "We know Labour has let our Jewish supporters and members down by failing to eradicate the anti-semitism within our ranks.
"Each of us recognises the leadership role we must ourselves play in addressing this toxic racism; calling out those who seek to make solidarity with our Jewish comrades a test of foreign policy and proudly standing with them in saying and acting to ensure anti-semitism has no place in the Labour movement at any level."
However, in a thinly-veiled swipe at the Labour leadership, the peers said that "words mean little when not backed by deeds".
And they added: "Therefore we pledge to join and encourage our colleagues both here in the House of Lords and in our local parties to join JLM, to speak up against anti-semitism wherever it is expressed without fear or favour and to recognise JLM, who have been affiliated to the Labour party for 99 years, as the legitimate and long-standing representative of Jews in the Labour party."
A Labour party spokesperson said: "Jeremy Corbyn and the Labour Party are fully committed to the support, defence and celebration of the Jewish community, and we have sped up and strengthened our processes for dealing with complaints.
"Anti-semitism complaints received since April 2018 relate to about 0.1% of our membership, but one anti-semite in our party is one too many.
"Jeremy Corbyn has written to JLM expressing his determination to work more closely with them to root out the evil of anti-semitism from our party and wider society."
Earlier this month, JLM members agreed by a show of hands to remain affiliated to the Labour party. A full ballot will take place in April.
A fresh row erupted days later when it emerged the JLM would no longer be providing anti-semitism training for party members.
Labour confirmed that the courses will be provided by academics at Birkbeck in the University of London instead.