Archbishop Diarmuid Martin has warned that one of the country's largest charities, Crosscare, does not have enough food to meet demand.
The Dublin diocesan social care agency has said unless parishes provide urgent help, more hungry people could be turned away soon.
It was an unprecedented appeal for food from Archbishop Martin, delivered at a mass marking the feast-day of Dublin's patron saint, Laurence O'Toole.
He said that Crosscare supplies food directly to people in need as well as to ten other charities, including the Society of St Vincent de Paul in Dublin and Co Wicklow.
Archbishop Martin said this year it expects to have distributed 750 tonnes of food, 50% more than last year.
He warned that demand for basic items is outstripping supply.
He cited the example of one unidentified community where, last week, Crosscare could provide only 40 food parcels where 120 were needed.
Crosscare said it will be sending collection vans to parishes each week during December.
Among its urgent requirements are pasta and rice, fruit juice, tea and coffee, soup, sugar and powdered milk, canned meat, fish, vegetables and fruit, as well as packaged desserts and biscuits and hygiene products.