Several American Jewish groups plan a major rally outside the United Nations on September 22 to protest against Iranian President Mahmoud Ahmadinejad.
Organizers said Tuesday that both Clinton, who nearly won the Democratic nomination for president, and Palin, Republican candidate John McCain's running mate, are expected to attend.
That would have set up a closely scrutinized and potentially explosive pairing in the midst of a presidential campaign, one in which the New York senator is campaigning for Democratic nominee Barack Obama while Palin actively courts disappointed Clinton supporters.
Clinton aides were furious. They first learned of the plan to have both Clinton and Palin appear when informed by reporters.
"Her attendance was news to us, and this was never billed to us as a partisan political event," said Clinton spokesman Philippe Reines. "Senator Clinton will therefore not be attending."
A McCain-Palin campaign official, speaking on condition of anonymity because Palin's schedule for Monday has not been announced, said only that Palin tentatively planned to attend the rally.
Malcolm Hoenlein, executive vice chairman of the Conference of Presidents of Major American Jewish Organizations, did not immediately return messages Tuesday seeking comment, nor did other organizers of the rally. Other event sponsors are the National Coalition to Stop Iran Now, United Jewish Communities and the Jewish Community Relations Council of New York.
Both McCain and Obama have made strong appeals to Jewish voters, particularly in critical states like Florida. Obama has emphasized to Jewish audiences his commitment to Israel's security, and has worked to dispel doubts created by false rumors that he is Muslim.