Israeli and Palestinian rights groups went to Israel's Supreme Court on Monday in a bid to stop the army's use of lethal force against Palestinians during protests and clashes on the Gaza border.
Forty-eight Palestinians have been killed by Israeli fire on the frontier since the start of protests that organisers have dubbed the Great March of Return on March 30, with more than 1,500 wounded.
No Israelis have been hurt.
The army has accused Hamas, the Islamist group that runs Gaza and has fought three wars with Israel since 2008, of seeking to use the protests as cover to carry out attacks.
Five Israeli NGOs and the Gaza-based Al Mezan Centre for Human Rights argued that international law bars the use of lethal fire against unarmed demonstrators.
The Israeli government's written response to the petitions says the Gaza protests are not peaceful civilian demonstrations but "part of the armed conflict between the state of Israel and the Hamas terrorist organisation."
It adds that live fire is only used as a last resort after non-lethal means have failed to stop actions it considers "a real danger" to Israeli troops and civilians living near the border with Gaza.
Speaking in the packed Jerusalem courtroom Monday, attorney Suhad Bishara, representing Israeli rights group Adalah, said the facts indicated otherwise.
"The great majority of those shot were at a distance from the (border) fence," she said.
"There is systematic use of lethal fire with no justification."
The army's rules governing use of live fire are officially classified but widely known in a country where most Israelis perform compulsory military service.
"What we know is that the Israeli army has tailored a new type of rules of fire regulation which do not meet international standards," lawyer Michael Sfard, for the other Israeli NGOs, told reporters after the hearing.
"Israeli case law is very clear that rules of engagement are secret and privileged," he said.
"But we know enough about them to argue that these sections which allow lethal force against unarmed civilians who do not pose danger are illegal. This is the crux of the case."
The government response says the open-fire regulations "conform to international law as well as Israeli law, including the Supreme Court's jurisprudence".
The judges gave each side until May 6 to submit written precedents in support of their arguments, after which it will deliver its ruling.
The European Union and UN chief Antonio Guterres have called for an independent investigation into the deaths, but Israel has rejected the idea.
The United States, Israel's strongest backer, has blocked moves for a probe at the United Nations.