An Egyptian court has overruled a controversial 20-year deal on gas exports to Israel.
Judges ruled in favour of Ibrahim Yousri, a lawyer who says that Egypt is losing $9m for each day that Cairo upholds the fixed-price agreement with Tel Aviv.
Many Egyptians view the gas deal with their former enemy as a betrayal, although Tuesday's court ruling can be appealed against by the government.
"Ibrahim was supported by other political activists who think that exporting gas to Israel helps the Israeli army continue its occupation of Palestinian territories," Amr el-Kakhy, Al Jazeera's correspondent in Cairo, said.
Egypt began to pipe natural gas to Israel in May, in line with a 2005 agreement to deliver 1.7 billion cubic metres of gas per year.
In recent months, Ahmed Mohamed Nazif, Egypt's prime minister, has signalled that Cairo wants to increase revenues from its energy exports amid the rising cost of gas, although he has not explicitly referred to the deal with Israel.
Private media organisations and opponents of the Egyptian government have led calls for Cairo to raise its prices for the gas it delivers to Israel.
"According to some experts and analysts here in Egypt, the country pledged to supply Israel with petrol and oil from Sinai in the Camp David peace treaty [between Israel and Egypt in 1979]," our correspondent said.
"When Egyptian oil supplies began to run out three or four years ago, Israel stepped in and demanded the export of gas.
"This is why the Egyptian government went into this memorandum of understanding with the Israeli government. It was not subject to approval by the Egyptian parliament – this is what has angered activists here."
Anti-Israel sentiment is still pervasive in Egypt, 29 years after the two countries signed a US-backed peace treaty.
Egypt and Israel fought against each other in four wars between 1948 and 1973.