The JNF came under renewed attack this week from anti-Zionists calling for the removal of its charitable status.
Veteran activist Uri Davis - author of Israel: An Apartheid State - addressed a "Stop the JNF" meeting organised by the International Jewish Anti-Zionist Network (Ijan) at London's School of Oriental and African Studies on Tuesday.
Michael Kalmanovitz, an Ijan UK co-ordinator, said the event was "part of a campaign to expose the role of JNF and to protest at its fundraising activities".
The campaign, subtitled "Stop greenwashing apartheid", wants to see the JNF derecognised as a charity "across the globe" .
Mr Kalmanovitz also said: "We are urging organisations that collaborate with JNF to break their links, especially organisations that have anti-racist or environmental credentials."
He accused the JNF of having built over "stolen Palestinian land in order to hide villages that have been ethnically cleansed" and of currently displacing Bedouins in the Negev to make way for Jewish settlements.
But Samuel Hayek, chairman of JNF - whose listed honorary patrons include Prime Minister David Cameron as well as predecessors Gordon Brown and Tony Blair - rejected the accusations as "groundless" and "part of a campaign to delegitimise Israel".
Mr Hayek said the campaign against his organisation was not new. "While they continue to make accusations, we continue to build reservoirs and plant trees. We are proud of our ecological work for the people of Israel over the past 100 years."
Tuesday's meeting was sponsored by a coalition of organisations including the SOAS Palestine Society, Jews for Boycotting Israeli Goods and "Rabbis for Palestine" (which is linked to the extreme Neturei Karta sect).
Dr Davis, who converted to Islam before his marriage to a Palestinian woman two years ago, is a member of the Fatah Revolutionary Council and describes himself as a "Palestinian Hebrew of Jewish origins". He was a prominent figure in UK anti-Zionist circles before returning to Israel in the 1990s.
His website contains a section on the JNF which claims that the organisation is implicated in "Jews-only" land policies that are "worse" than the former apartheid regime in South Africa.
He is also the editor of a new online booklet targeted at the JNF in Canada.
As well as Ijan, the Stop the JNF campaign is endorsed by the Palestinian BDS (boycott, divestment and sanctions) National Committee and the Scottish Palestinian Solidarity Campaign.