A prominent Manhattan synagogue has dispelled reports that New York City’s mayoral frontrunner, Zohran Mamdani, will be joining the congregation for Yom Kippur services, marking a setback for the Democratic socialist as he seeks to win over skeptical Jewish voters.

Congregation B’nai Jeshurun — a non-denominational synagogue in uptown Manhattan — became the subject of speculation this week after the New York Times reported that Mr. Mamdani “intends to join” Representative Jerry Nadler for services at a “mainstream congregation” on the Upper West Side.

Mr. Nadler, the most senior Jewish member of Congress, has been a longtime congregant at B’nai Jeshurun and has attended services there during the High Holy Days in previous years. He was among the first Democratic lawmakers to endorse Mr. Mamdani following his upset primary victory over Governor Andrew Cuomo.

This week, however, B’nai Jeshurun informed its members that “Assemblymember Mamdani will not be joining services with our community,” according to an email message the synagogue sent on Thursday. “Yom Kippur is a holy day of deep spiritual significance, of introspection and prayer, not a time for political campaigning.”

B’nai Jeshrun aligns with left-wing politics and its leaders have been vocal in their support for Palestinian statehood. In June, the congregation hosted Mr. Mamdani and other mayoral candidates for a forum on issues affecting the Jewish community. 

The congregation, however, embraces Zionist principles, stating that “Israel is at the center of the Jewish narrative and Jewish identity.” The synagogue also organizes trips to Israel. 

Mr. Mamdani, by contrast, has publicly identified as an anti-Zionist and has declined to explicitly affirm Israel’s right to exist as a Jewish state. His positions on Israel have divided New York City’s Jewish community and raised concerns among many of the city’s Jewish leaders.

As the general election approaches, Mr. Mamdani has sought to heal this rift, and the 10-day period of the Jewish High Holy Days offered the assembly member an ample opportunity. For Rosh Hashanah, which began on Monday evening, Mr. Mamdani attended services with ally Brad Lander, the city comptroller, at Kolot Chayeinu, one of Brooklyn’s most liberal synagogues.

The non-denominational Park Slope congregation has faced criticism for its anti-Zionist stance and highly politicized programming surrounding the Israeli-Palestinian conflict. In 2024, the synagogue extended an interim position to transgender activist Rabbi Abby Stein, a member of the anti-Zionist group Jewish Voice for Peace.