The Jewish Labour Movement has called in the police to investigate its finances, members were told late on Wednesday night.
In an email circular, it said it had taken steps over the past week to ensure its financial governance met "the highest standards" expected by members and instigated an external review of its accounting and procedures, as well as taking legal advice.
It said in order "to ensure full transparency, openness and to protect the integrity of the movement, we have referred certain internal financial matters to the police for investigation".
But it said it would "not be appropriate for us to make any further comment" at the present time.
The email came from national secretary Peter Mason after an emergency meeting of its national executive earlier on Wednesday evening.
Mr Mason said the movement would shortly hold its annual meeting where it would elect a new chairman and receive its audited accounts.
At the time of writing, it was unclear if this investigation concerned Jeremy Newmark, the former JLM chair.