The Israeli chief rabbis have issued a statement urging Jews to stay away from an upcoming Christian conference they described as a “spiritually dangerous” event that undermines the Jewish faith.

In a letter dated September 3, Ashkenazi Chief Rabbi David Lau and Sephardic Chief Rabbi Yitzhak Yosef charged that the annual event organized by the International Christian Embassy in Jerusalem was a missionary effort to convert Jews to Christianity.

“This is a grave matter that runs contrary to our faith, and we must therefore denounce it and warn the public,” the letter read.

While the rabbis noted the staunchly pro-Israel ICEJ were friends of the Jewish state, they said that the gathering at Jerusalem’s Pais Arena intentionally targeted Israeli Jews with missionary activities.

“We call on the Jewish community in the Holy Land not to take part in this conference… the event is spiritually dangerous and undermines the nature of Judaism,” Lau and Yosef wrote.

Christian pilgrims at a Feast of Tabernacles event at Jerusalem's Pais Arena. October 13, 2014. (Courtesy ICEJ)

Christian pilgrims at a Feast of Tabernacles event at Jerusalem’s Pais Arena. October 13, 2014. (Courtesy ICEJ)

Conference organizers, the rabbis said, were actively “engaged in missionary work on behalf of the ICEJ.”

The ICEJ’s week-long conference — titled The Feast of Tabernacles and set to coincide with the Jewish festival of Sukkot — draws thousands of evangelical Christians who celebrate the organization’s declared unshakable bond with Israel. In 2014, some 5,000 Christian pilgrims from 80 different countries filled the seats of the Pais Arena.

ICEJ raises millions of dollars to assist with the immigration to Israel of Jews from around the world, most recently from India and Ukraine. During last summer’s conflict between Israel and Hamas in Gaza, the organization provided portable bomb shelters and other assistance to Israeli communities on the Gaza border. The organization also runs a full-care residence for 70 Holocaust survivors in Haifa.

During one night of the conference, dubbed “Israeli Night,” attendees honor Israeli soldiers and survivors of terror attacks, and in 2014, some 300 Jewish, Christian and Druze IDF paratroopers who served in Gaza were invited as special guests.

Thousands of Evangelical Christians participating in an annual parade in Jerusalem to support Israel during the 2006 Sukkot holiday. (Olivier Fitoussi/Flash90)

Thousands of Evangelical Christians participating in an annual parade in Jerusalem to support Israel during the 2006 Sukkot holiday. (Olivier Fitoussi/Flash90)

According to ICEJ’s website, the Feast of Tabernacles is meant to celebrate the “recognition of the hand of God in Israel’s modern day restoration and the need to work with what God is doing, and bless it.” Last year’s feast was the largest in seven years, despite Israel’s conflict with Gaza, which ended less than two months before the conference.

“It’s an encouraging statement of solidarity,” ICEJ media director David Parsons told The Times of Israel in an interview last year.

The spirited, colorful, music-filled extravaganza includes visits to holy sites and study and prayer sessions for the pilgrims. They also participate in a march through Jerusalem to show solidarity with Israel.

Last year, President Reuven Rivlin, World Jewish Congress President Ronald Lauder, and Prime Minister Benjamin Netanyahu addressed conference attendees, thanking them for their support of Israel.

In concluding their statement, the Israeli chief rabbis reiterated that Jewish participation in the ceremony was strictly forbidden by the Torah.

Last month, a number of rabbis petitioned the owner of the arena, asking for the names of the slated speakers in order to “prevent inappropriate missionary activity,” the ultra-Orthodox news site Kikar Hashabbat reported. The rabbis said they objected to the conference after learning that IDF soldiers would be in attendance.

Renee Ghert-Zand contributed to this report.