A worker loads humanitarian aid on a truck at the Kerem Shalom crossing between southern Israel and the Gaza Strip. AFP
Describing the GHF as a private security company, it said aid distribution should be left to UN organisations and humanitarian agencies.
"The dire humanitarian situation in Gaza requires an immediate response," TRIAL International's executive director, Philip Grant, said in a statement.
"However, the planned use of private security companies leads to a risky militarization of aid," he added.
That, he argued, "is not justified in a context where the United Nations and humanitarian NGOs have the impartiality, resources and expertise necessary to distribute this aid without delay to the civilian population."
TRIAL International said it had filed legal submissions calling on Switzerland, where GHF is registered, to check that the group was complying with its own statutes and the Swiss legal system.
The GHF has said it will distribute some 300 million meals in its first 90 days of operation.
But the United Nations and traditional aid agencies have already said they will not cooperate with the group, which some have accused of working with Israel.
On Thursday, the UN cited concerns about "impartiality, neutrality (and) independence."
Aid began trickling into the Gaza Strip this week for the first time in nearly three months, amid condemnation of the Israeli blockade that has sparked severe shortages of food and medicine and exacerbated an already dire humanitarian crisis.
On Friday, Gaza's health ministry said at least 3,673 people had been killed in the territory since Israel resumed strikes on 18 March, unilaterally ending a two-month ceasefire in its war on Gaza.
This brings the total death toll to 53,822. However, the Gaza government media office's updated toll now stands at more than 61,700, as it includes thousands still trapped under rubble and presumed dead.
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