|Egyptians walk by a giant poster of President Hosni Mubarak that says: "we support you, we pledge our allegiance to you"|
The government of President Hosni Mubarak says the amendment honors its pledge of reform and clears the way for a contested presidential election in September.
Egypt's state-media urged voters to participate in the refrendum. But opposition groups appealed for a boycott, arguing that the proposed changes are so narrow they will not allow any serious challenges to the ruling National Democratic Party.
The amendment needs support from at least 51 percent of voters. More than 30 million Egyptians are eligible to vote.
On Tuesday, authorities detained more than a dozen activists - mostly members of the Muslim Brotherhood - who were campaigning for a boycott of the referendum.
Some information for this report provided by AP and Reuters.