ALEXANDRIA, Egypt — Demonstrators in Egypt have protested against rising prices and stagnant incomes, for greater freedom and against police brutality. But religion, so often a powerful mobilizing force here, has so far played little role.

That may be about to change.

With organizers calling for demonstrations after Friday prayer, the political movement will literally be taken to the doorsteps of the nation’s mosques. And as the Egyptian government and security services brace for the expected wave of mass demonstrations, Islamic groups seem poised to emerge as wildcards in the growing political movement.

Reporters in Egypt said on Friday that, after rumors swept Cairo late Thursday that the authorities planned to throttle the protesters' communications among themselves, access to the Internet, text messaging services and Twitter was not possible on Friday morning in Cairo, Alexandria and possibly other cities.

Heightening the tension, the Muslim Brotherhood, the largest organized opposition group in the country, announced Thursday that it would take part in the protest. The support of the Brotherhood could well change the calculus on the streets, tipping the numbers in favor of the protesters and away from the police, lending new strength to the demonstrations and further imperiling President Hosni Mubarak’s reign of nearly three decades.