The supporters of the Hizb al-Amal, or Labour Party, on Monday chanted slogans against the president in front of parliament, some wearing badges that read "No to Mubarak", a sign of defiance unthinkable a few months ago.
The demonstration ended peacefully but came amid an intense debate in Egypt after an announcement by Mubarak in late February that an amendment to the constitution would be made to allow multi-candidate presidential elections.
The move was widely hailed as a landmark step towards democracy, but opposition members have warned that the restrictions imposed by Mubarak will effectively strip the reform of credibility.
"We have obtained a victory by getting rid of the referendum but the proposal made in parliament on Monday goes against the will of the people," said a leaflet distributed at the protest.
"The government has limited the number of possible candidates to three or four known figures. The result will be a masquerade giving Mubarak the pretence of having been elected by the people," it warned.
There have been no competitive elections in Egypt since the 1952 military coup that toppled the monarchy.