The law, which seeks to prevent imprisoned Palestinian militants from pressuring Israel by refusing food, was initially approved by cabinet in June 2014 at the height of a mass hunger strike of Palestinian prisoners, during which dozens were hospitalised.
While the law does not specifically mention Palestinians, Internal Security Minister Gilad Erdan, who led the legislation, said it was necessary since "hunger strikes of terrorists in prisons have become a means to threaten Israel."
The law, which passed by 46 votes to 40, "will be used only if a doctor determines that the continued hunger strike will create an immediate risk to the life of a prisoner or long-term damage to his health," David Amsalem of the ruling Likud party said.
But opposition members decried the new measure, with the Arab Joint List of parties criticising "a law to torture Palestinian prisoners, aimed at uprooting their legitimate struggle".
It said the law reflected Prime Minister Benjamin Netanyahu's government's "distorted take on fundamental democratic values."
The law had been vehemently opposed by the Israeli Medical Association, which warned it would "order doctors to act solely according to the rules of ethics, and not feed or nourish hunger strikers against their will."
According to the Association for Civil Rights in Israel, the majority of prisoners who go on hunger strike are Palestinians in administrative detention, under which they held for renewable six-month periods without charge.
The association was among 10 rights groups which warned on Wednesday that the law's sole aim was "to break the spirit and body of administrative detainees and prisoners expressing protest in a non-violent way."
On Tuesday, United Nations special rapporteur on torture Juan Mendez and UN special rapporteur on the right to health Dainius Puras called on Israel to halt the legislation.
"Feeding induced by threats, coercion, force or use of physical restraints of individuals, who have opted for the extreme recourse of a hunger strike to protest against their detention, are, even if intended for their benefit, tantamount to cruel, inhuman and degrading treatment," Mendez said in a statement.
"The way to end the hunger strikes is not to force feed hunger strikers but to address the underlying human rights violations against which they are protesting, namely, the practice of administrative detention."
A spokeswoman for the Israel Prison Service said there was currently one Palestinian held on administrative detention and four "security prisoners" who had been on hunger strike for over a week.
Editor: Ade P Marboen
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