Jewish Care chairman Steven Lewis has accused British Jews of being more "materialistic and selfish" than ever before.
Mr Lewis, who has chaired the UK's largest communal welfare organisation since 2011, said: "I think we live in a society that is materialistic, which has become more selfish.
"I know a lot of people who don't give tzedakah - time or money. They give a few quid here or there and think they've done their bit. They have lavish barmitzvahs and unbelievable holidays. I find that unacceptable."
Mr Lewis said that such people were betraying Judaism: "If you don't understand giving time or money, I don't think you're acting responsibly as a Jewish person."
Mr Lewis's comments came despite an increase in individual donations to Jewish Care last year. Income fromfundraising initiatives and individual pledges was up by £1 million.
They give a few quid and then have lavish barmitzvahs. It is unacceptable
But, also last year, the welfare charity saw legacy income fall from £4.5m to £2m.
A Jewish Care spokeswoman said the fall in legacy donations had affected all Jewish charities and meant Jewish Care was £1.5m short of its £15m annual target.
She added: "The reduction in legacy funding coupled with decreases in government funding due to pressures on social care services means we have to rely more than ever before on the generosity of the whole community."
Mr Lewis said: "I was always told that 10 per cent is the level you give to tzedakah. It's fair to say that if everyone gave 10 per cent of what they earned, we would have far more vibrant organisations."
He also attacked public disagreement between senior leaders in the community as "upsetting".
This year, Mr Lewis signed a letter denouncing JNF UK head Samuel Hayek, after Mr Hayek attacked JLC chairman Mick Davis for criticising the Israeli government.
Mr Lewis said: "We're a very small community and [should] find common themes to work together.
"That's why I get upset when some of the big machers in the community have a row. I say, 'you're the good people - argue with people who sit on the sidelines and do nothing'."