Nabil Abu Rdeneh said President Mahmoud Abbas had a long phone conversation with Obama on Sunday evening.
He said Obama "expresses his opposition to this step," but Abbas replied he would carry on.
In Washington, the White House press office said that Obama "reiterated the United States' opposition to unilateral efforts at the United Nations."
Obama also "reaffirmed his commitment to Middle East peace and his strong support for direct negotiations between Israel and the Palestinians" for a peace accord, the White House said.
The U.S. and Israel have opposed upgrading the Palestinian status at the world body to nonmember observer state.
Israel and the U.S. say a Palestinian state can be established only through negotiations.
Talks broke down four years ago over the issue of Israeli settlement construction in lands the Palestinians claim for a state.