Every year, evangelical Christians descend on Jerusalem for the Feast of Tabernacles or Sukkoth. It is promoted by the International Christian Embassy Jerusalem, which this year held a convention in Jerusalem attended by thousands of Christian Zionists.

While it has become a fixture in the calendar of many Israel-supporting evangelicals, many Jews are far less enthusiastic about Christian participation in the event, regarding it as disguised missionary activity.

Ashkenazi Chief Rabbi David Lau and Sephardi Chief Rabbi Yitzhak Yosef told Orthodox Jews in Israel they should not accept the invitation to attend.

They said: "To our brethren of the House of Israel we will say: Do not join this assembly, whose purpose is to prevent the true redemption of Israel. According to our holy Torah, we must keep away from this event, and it is forbidden to join them in any way."

An Al-Monitor article cites ultra-Orthodox Jewish organisations which aim to combat the Christian Zionist agenda through protest, education and if necessary legal action.

One of them, Yad L'Achim, has the strapline "We don't give up on a single Jew". It believes that the Sukkoth observation is an attempt to proselytize about Christianity. Its head, Rabbi Shmuel Lifschitz, told Al-Monitor: "For years we had a tacit understanding with the International Christian Embassy in Israel, whereby they steered clear of missionary activity, and over the years, they did keep their part of the deal.

"However, last Sukkoth, they hosted soldiers and young Jews and openly preached for conversion to Christianity. As far as we are concerned, it was crossing a red line."

The Christian Embassy did not respond to Al-Monitor's request for comment on the matter, but has previously said that it does not proselytise.

Lifschitz has called for a law to strengthen a 1977 law banning missionary activity involving "material benefit" and activity among minors, which he says is not adequately enforced because of concerns that it would antagonise the Christian world. He accused missionaries of "deceptive" tactics in giving Jewish passers-by books of Psalms and prayer shawls with evangelistic literature inside. "We are promoting legislation that would force the due diligence marking of those materials as Christian," he told Al-Monitor.

Yad L'Achim's website carries headlines such as "Missionaries strike again: Campaign targets Israel's south", about a Jews for Jesus billboard campaign featuring Christian messages at traffic intersections and the distribution of flyers at traffic lights. It sends teams to counteract the missionaries' activities, describing the evangelists' work as a "spiritual assault on the Jewish people".

Yad L'Achim has taken up the cause of postmen in Ashkelon, who objected to delivering missionary material to homes as part of their work. One of its legal advisers, Moshe Morgenstern, argued that distribution of the flyers, in Hebrew and Russian, was a violation of the law banning attempts to entice minors to convert. He said that children, who arrive home from school before their parents and collect the mail, are the first to be exposed to the material. Israel Post declined Yad L'Achim's request that the deliveries should be suspended.

The organisation was founded in 1950 to help new immigrants adjust to life in Israel. However, it says: "Over the years, its attention has turned to more complex problems, including how to counter the missionary threat...Fighting the missionaries, who have millions of dollars a year at their disposal, has long been one of Yad L'Achim's top priorities."