An Istanbul high court held a hearing on Wednesday of Israeli flotilla raid in 2010, that killed 10 people.
But victims of the raid fear the court may halt the case brought by them because of a deal to restore ties between Israel and Turkey, a lawyer representing the victims said on Monday.
The deal requires Turkey pass legislation protecting Israeli soldiers against fortilla raid lawsuits.
"The so-called agreement between Israel and Turkey is not a treaty that is enforceable. It is unlawful under international law, under the European Convention of Human Rights and under the Turkish law " Rodney Dixon, a human rights lawyer said.
Dozens of pro-Palestinian activists gathered outside the courthouse ahead of the court session waving Palestinian flags and placards.
"I can tell you that Palestinians in Palestine are watching this case." said Zuneida Awal, a pro-Palestinian activist.
Israel, which had already offered apologies for the raid - one of Ankara's three conditions for a deal - agreed to pay out $20 million to the families of those killed.
"We are well aware that Israel was expecting Turkish court to halt the case. Twenty million dollars is not admission of liability, it is a donation," Bulent Yildirim, chairman of the Humanitarian Relief Foundation (IHH) that organized the flotilla, told the crowd.
Relations between Israel and what was once one of its Muslim allies crumbled after Israeli marines stormed the Mavi Marmara ship in May 2010 to enforce a naval blockade of the Gaza Strip.
The Mavi Marmara was part of a larger aid flotilla and the court case has been brought on behalf of hundreds of people who say they were wounded, assaulted or imprisoned during the raid.
According to the deal, the naval blockade of Hamas-run Gaza, which Ankara wanted lifted, remained in force, but humanitarian aid was to keep going into Gaza via Israeli ports.