http://pjmedia.com/blog/pleading-for-end-to-israeli-concessions-rabbis-reference-jewish-law/?print=1
New Israeli concessions and the resumption of talks with the Palestinian Authority are tragedies, replays of the Oslo process of the 1990s and the Gaza disengagement. Both of those events not only failed to bring peace, but simply made matters worse.
Many rabbis have since called on the Israeli government not to give in to concerted international pressure. The rabbis plea is not merely strategic: it is based upon Jewish law – Halacha — and centers around an explicit ruling in perhaps the most authoritative text on contemporary Jewish law. The Shulchan Aruch rules against giving away land in border communities that are under attack.
In Orach Chaim (329:6), the section dealing primarily with the laws of the Sabbath and festivals, the Shulchan Aruch tackles the question of whether Jewish communities anywhere in the world that find themselves under siege or attack on the Sabbath can violate the holy day to wage war. The ruling states:
If their [the attackers] intent was financial gain, the Sabbath laws should not be violated because of them.
…
[However] if their intent was against Jewish lives, or if they lay siege without any stated intention, or if there is a sense that they are coming for Jewish lives, then even before they come — and are only mobilizing themselves — it is a mitzvah [Torah commandment] to go out and attack them with weapons of war and violate the Shabbat laws.