Taoiseach Enda Kenny has warned Irish human rights activists against trying to break the blockade of Gaza.
The Irish-owned MV Saoirse is at an undisclosed Mediterranean port waiting to sail with other international aid vessels as part of Freedom Flotilla II.
Mr Kenny said the Government was strongly advising against the trip while Israel's naval forces continue to enforce the blockade.
But Socialist Party TD Joe Higgins hit out at the Taoiseach, first accusing him of cowardly capitulating to Israel before describing him as "pathetically weak" in diplomatic efforts to allow humanitarian aid through.
"What you have just said is a disgusting and cowardly capitulation to the pressure of the Israeli Government," Mr Higgins said.
"It's a disgrace that an Irish prime minister, Taoiseach, would stand up and discourage humanitarians bringing critically needed supplies to a besieged people."
Tanaiste Eamon Gilmore said he has told Israeli Ambassador to Ireland, Boaz Modai, that any interception of the flotilla must be peaceful.
Mr Kenny urged the Israeli government not to take action that would cause harm to the activists.
But he said: "The advice, while respecting the motives of the participants here, is not to travel to Gaza while this blockade is in force."
Nine people were killed last year when commandos stormed the MV Marmara, a Turkish aid ship trying to break the naval blockade.