The Board of Deputies and strictly Orthodox charity Interlink have joined a coalition of Christian groups in opposing welfare cuts, which they say will hit large families.
A briefing paper prepared for the House of the Lords, which is due to discuss the proposal next week, describes the measures as "fundamentally anti-family".
Their concern has been triggered by plans in the Welfare Reform and Work Bill to limit low-income families to claiming tax credits for no more than two children.
A Board spokesman said that "this will adversely affect thousands of Jewish children in working households, with the pain being felt particularly in the Charedi community".