Police blocked opposition supporters from protesting outside the Egyptian parliament on Tuesday following the assembly's adoption of a set of constitutional amendments the opposition has denounced as a blow to democracy. The area around the parliament was sealed off by police officers and plainclothes police agents. Several dozen demonstrators then reconvened outside the press syndicate in downtown Cairo. Police said six activists were arrested, and the protesters said they included two pro-reform bloggers. President Hosni Mubarak on Tuesday set a popular referendum to vote on the amendments for March 26, more than a week earlier than expected. The move prompted opposition accusations the government was deliberately speeding up the process to prevent them from organizing a "no" vote. Some opposition members promptly called Tuesday for a boycott of the referendum. But the Muslim Brotherhood - Egypt's largest opposition movement - said it might call instead for its supporters to show up at the polls and vote against the measures. The head of the Brotherhood's political bloc, Mohammed Saad el-Katatni said the group would decide within a day whether to boycott or participate in the referendum. The government and ruling party have said the amendments are part of a reform package aimed at increasing democracy in Egypt, where the 78-year-old Mubarak has ruled unchallenged for a quarter century. But the opposition says the changes are aimed at ensuring the ruling party's lock on power, part of what they call a plan by Mubarak to ensure that his son, Gamal, succeeds him in a future election. The opposition says the amendments will restrict judicial supervision of elections they deem vital to preventing vote fraud. Strong presidential security powers are also written permanently into the charter, which they fear will be abused. The 454-seat parliament approved the 34 amendments late Monday after a marathon discussion that the opposition boycotted, though it joined in the final vote. The amendments passed with 315 votes in favor and 113 votes against. A spokesman for the Muslim Brotherhood, Hamdi Hassan, accused the government of passing the measures "in the night, like thieves" and said the manner of the vote "reveals the extent of the conspiracy against the people." Opponents also believe the amendments aim to ward off any election challenge from the Islamic fundamentalist Muslim Brotherhood. The group scored a surprise victory in 2005 parliamentary elections, winning about a fifth of the seats. One amendment bans the formation of any political party based on religion, ensuring the Brotherhood - which is banned - cannot become a party. Another amendment would require any candidate for president to come from a recognized political party holding at least 3 percent of the seats in parliament, ensuring an independent cannot run. Brotherhood candidates run as independents in elections. The opposition was also angered by a change that would create an independent commission to monitor elections, a step they say will reduce the role of judges in overseeing the vote. During the 2005 elections, pro-reform judges blew the whistle on vote fraud that plagued the balloting. Another amendment would replace emergency laws in place since the 1981 assassination of President Anwar Sadat, which give police wide powers to detain people and curb political activity. Under the new proposed amendment, the constitution would empower the president to refer "any terrorist crime to any of the judiciary authorities stated in the constitution or the law." Opponents say that means the president can refer suspects to military courts, which have been widely used in the past but are sharply criticized by rights groups since their rulings cannot be appealed. The London-based rights group Amnesty International said the proposed reforms, particularly the anti-terrorism statute, will lead to the "greatest erosion of rights in 26 years." Foreign Minister Ahmed Aboul Gheit has bluntly rejected the criticism, saying outsiders don't have the right to "even express their opinion" on Egypt's constitution.