A court in Egypt has ordered the government to suspend gas exports to Israel, although it is not clear whether the ruling will be heeded, reported BBC.
It started piping gas to Israel earlier in 2008 under a deal to supply 1.7bn cubic metres a year over 20 years.
But the court said the deal should been put before Egypt's parliament before being finalised.
There has been widespread opposition in Egypt to the exports because of Israel's treatment of the Palestinians.
Many take issue with Israel's continuing blockade of the Gaza Strip, where food and fuel supplies have been severely restricted.
Correspondents say the government in Cairo may challenge the ruling or merely ignore it, as it has done on several other issues.
"The People's Assembly is the body best qualified to monitor the actions of the administration with regards to granting concessions to exploit natural wealth," the court said in quotes carried by the state news agency Mena.
Egypt was the first Arab country to sign a peace deal with Israel - the 1979 Camp David accords - but relations have remained strained over the Israeli-Palestinian conflict and other regional issues.
In addition to political objections, Egyptian activists have said Israel is buying the gas at prices below the international level.
Egyptian petroleum officials have not commented on the ruling, but Israel's infrastructure ministry said it had "no doubt" the gas deal remained valid.