“The three parties announce that they will boycott the May 25 referendum on the constitutional amendment and call on the Egyptian people to boycott it and stay home that day,” the parties said in a joint statement.

The center-liberal Wafd, the Marxist party Tagamu and the Nasserist Party charge that the new conditions for registration are so strict that only the ruling National Democratic Party (NDP) will be able to field a candidate, undermining the whole point of the reform.

The Muslim Brotherhood later issued a statement in which it called for a boycott “in agreement with the position of parties and national political forces which refuse to participate” in the referendum.

The group has been banned since 1954 but has 17 MPs sitting as independents in parliament. Egyptian analysts estimate it could snatch as many as 30 percent of seats in free and fair elections.

Egypt’s lawmarkers, facing mounting calls for reform from both institutional parties and other secular and Islamist opposition groups, approved the amendment on May 10.

Under the proposed changes applying to the next polls due in September, independents must collect 250 signatures from MPs, senators and representatives in local councils which are dominated by President Hosni Mubarak’s NDP.

The following elections in 2011 will further require that political parties field candidates only five years after coming into existence. They should also hold a minimum of five percent of seats in both houses of parliament.

Wafd, Tagamu and the Nasserist Party also announced they would no longer take part in a dialogue called by the NDP on democratic reforms backed by Washington.

“The NDP rejected every proposal advanced (by the opposition), notably pertaining to the constitutional amendment,” their statement read.