More than 1,000 prisoners - mostly Palestinians - held on "security" grounds will remain behind bars despite being due for release on Friday, after a change in legislation pushed by extremist Israeli National Security Minister Itamar Ben-Gvir.
A bill supported by Ben-Gvir and passed by the Knesset in July has excluded security prisoners from a law allowing for the early release of all prisoners with sentences of up to three years.
This was passed in a bid to tackle prison overcrowding and was set to come into effect on Friday.
The change to the law means that only 120 of around 1,500 prisoners will be released on Friday, according to Haaretz.
Ben-Gvir's change to the law has drawn opposition from Israel's Prison Service and Israeli internal security service Shin Bet.
Israel's current prison population of 16,279 - in excess of the standard of 14,500 set by the Knesset's Interior Committee.
At present levels, prisoners are also not given the minimum of 3.5 square metres as ordered by the High court of Justice.
Adalah, a rights group representing Palestinians in Israel, slammed Ben Gvir's change to the law as "racist".
"The law in question is another step up in the racist, sweeping and arbitrary measures against Palestinian prisoners," Adalah Attorney Rabia Agbaria said.
"The government which promoted this improper law is knowingly and deliberately acting in violation of the fundamental laws and in violation of the provisions of international law.
"This step is joined by the government's attempt to deepen the principles of apartheid in the Israeli prison regime, which is based on Jewish supremacy and two separate and discriminatory legal systems, and therefore we will demand its immediate cancellation."
There are 5,100 Palestinians jailed by Israel, with 1,200 held in "administrative detention", figures from prisoners' rights group Addameer show.
Administrative detainees have neither been charged with a crime nor granted a trial, and they and their lawyers are prevented from seeing evidence against them.
The detention orders typically last between three to six months and can be renewed indefinitely.
Palestinian prisoners have also long complained of abuse and neglect by Israeli prison authorities.