The Yugoslav student-based resistance movement Otpor staged a defiant but symbolic gesture after a police raid last week on its Belgrade headquarters, writes Gillian Sandford from Belgrade.
Anti-Milosevic actors, academics and lawyers restocked the office with T-shirts, pamphlets and leaflets.
The police arrested activists and confiscated computers and propaganda material exhorting Yugoslavs to vote against Milosevic in the forthcoming election.
Otpor activists said police broke into the private flat in Belgrade where they work and spent two hours removing material. "It was totally in breach of the constitution," said activist Slobodan Homen.
Raids also took place on offices in the northern city of Novi Sad and in Mladenovac, near Belgrade.
In a statement later that day, Belgrade police described Otpor as an "illegal, mercenary and pro-Nato" organisation. It added ominously: "All measures prescribed by law will be taken."
Spokesman Vukasin Petrovic said the police raids and the arrest for questioning of 25 activists showed that "the regime is done for and that it is panic-stricken over what the possible outcome of the September 24 vote may be."
"The police raid has neither scared us, nor prevented us from continuing with our activities," Mr Petrovic said.
Opposition politicians condemned the raid. Democratic Party vice-president, Boris Tadic said: "Milosevic knows he will lose the presidential election and now he is trying to avoid defeat by theft, arrests, political violence and total repression."
Otpor was formed out of the university students' movement of 1996-97 and still has a strong power base in the university towns of Novi Sad, Nis, Kragujevac and Belgrade. It has been increasingly active across the country in the run-up to the election.
The movement claims to have 70,000 activists in Serbia, many of whom have been subject to harassment by police.
Hundreds have been taken to police stations and held for what are termed "informative talks". Some allege they were beaten while in custody.