Egyptian police have clashed violently with protesters rallying in support of two senior judges who have been spearheading calls for reform.
Opposition groups report dozens of arrests by police
News agency reports said some people were beaten up and others detained as they tried to reach a court house where the judges faced disciplinary action.
Hesham Bastawisi and Mahmoud Mekki face dismissal for criticising last year's presidential election as fraudulent.
Mr Mekki told the BBC that the court action was illegal.
The two men refused to enter the court on Thursday when security services prevented many members of the defence team from coming in with them.
The Egyptian authorities have been facing an unprecedented challenge from the judiciary, who have become a rallying point for all those pressing for reform, says the BBC's Heba Saleh in Cairo.
The judges want new legislation guaranteeing their independence, and they have been speaking out against election-rigging, our correspondent says.
Large sections of central Cairo were sealed off by thousands of riot police armed with sticks and shields.
They brought traffic to a standstill while teams of plainclothes men beat up demonstrators, reporters said.
Three separate groups of activists, including a few hundred from the illegal Muslim Brotherhood, were attacked and dispersed by the police, they said.
The Muslim Brotherhood, the largest opposition movement in Egypt, said dozens of its members had been arrested. Secular opposition parties are also involved in the protests.
Several journalists were arrested briefly by police. The cameraman for the al-Jazeera news network was beaten and had his equipment confiscated.
Crowds of protesters have been chanting: "Judges, judges, save us from the tyrants."
Reports say five policemen were killed and 20 injured when their truck drove off a raised a causeway in Cairo.
The police were on their way to reinforce colleagues blocking the demonstrations in central Cairo.
The hearing against the men was delayed until next Thursday.
"A hearing which is controlled by the security forces and not the judiciary is null and void," Mr Mekki told the BBC.
Witnesses say police beat up protesters in Cairo
"It is absolute evidence of the lack of independence of the judiciary and the violation of justice in Egypt, unfortunately."
Mr Bastawisi echoed his comments. "This is not a trial, this is a scandal, so we protested and walked away," he told reporters.
"All those troops are not for our trial, it's because they are afraid of the nation. They are beating people up like mad in the streets.
"We won't attend until they stop those practices and release all those detained because of their support," he said.
Another condition, they say, is the release of all those arrested during previous weeks of protests in their support - about 50 since the first hearing two weeks ago.
The two judges are accused of damaging the reputation of the judiciary, working in politics and talking to the media.
The senior appeals court judges had published a report charging that there had been fraud and abuses in Egypt's two elections late last year.
The Egyptian President Hosni Mubarak says that he will not intervene in the case out of respect for the judiciary's independence.