Slobodan Milosevic's lawyer has filed a challenge with Yugoslavia's Constitutional Court, claiming a decree to extradite him to a war crimes court in The Hague is unconstitutional.
Mr Toma Fila, the head of Milosevic's 10-strong defence team, is demanding the constitutional court block the decree until it decides whether the measure is illegal.
The constitutional court judges will convene a council which has to decide whether the challenge has any legal basis or not, court officials said.
The UN war crimes court, based in The Hague, is seeking the ex-president for alleged war crimes committed in Kosovo during the 1998-99 war.
The United States and its allies have hailed the Yugoslav government decision to clear legal obstacles for the extradition of Milosevic and more than a dozen other war crimes suspects.
Yugoslavia risks losing billions of dollars in foreign money if it fails to co-operate with the court.
Some Serbian officials have suggested the appeals process could delay any extradition for more than two weeks. If extradited, Milosevic would be the first former head of state to face a war crimes trial in front of the UN court, established in 1992.
The decree was passed by the Yugoslav government on Saturday and took effect the following day. It was not immediately clear how soon any legal procedure for Milosevic's extradition will start.
Mr Fila, Milosevic's lawyer, criticised the measure as "legal piracy". He said Milosevic read the decree and also said it was illegal because nearly half of the ministers in the Yugoslav Cabinet were absent when it was agreed on.
PA