A copy of the latest poster appeared on the American website Failed Messiah.
Joanne Greenaway, the London Beth Din's get care-worker, said: "It is important to the London Beth Din to ensure that the get process is not abused and that those who do abuse it are held to account.
"We are really grateful for the support that rabbonim have shown in helping us to deal with this issue on the ground.
"We hope that it will lead to a positive result for Mrs Kahan, who has been prevented from moving on with her life for so many years."
But a friend of Mr Kahan, who is now based in New York, felt the condemnation was unfair.
He said that Mr Kahan had gone to the Beth Din of the Union of Orthodox Hebrew Congregations "as soon as he was back in London".
The friend added that Mr Kahan had "asked me to say he wants this matter settled, he wants to give a get, but outstanding matters have to be settled. He has taken halachic advice."
The two Batei Din, he said, "need to negotiate and discuss matters".
A spokesman for the Union rabbinate said that it fully supported the London Beth Din's action.
