Lithuania's Constitutional Court began impeachment hearings against President Rolandas Paksas on Tuesday after refusing a request by his lawyers to suspend all the judges for being partial.
It rejected the claim that an earlier ruling against Paksas could be interpreted as an expression of views by the judges.
The court ruled in late December that Paksas had breached the constitution by granting citizenship to the main sponsor in his election campaign, Russian businessman Jurijus Borisovas.
During Tuesday's hearing, broadcast on national television, one of the deputies who initiated the impeachment process, Raimondas Sukys, described the request for new judges as "just an attempt to extend the hearings."
The court decided to start a formal investigation of the charges that Paksas violated his oath of office, leaked classified information, meddled with private business, discredited public institutions and allowed his aides to abuse their powers.
Egidijus Kuris, the head of the court, said Paksas had "sent his explanations related to the accusations," and would be represented by three lawyers.
The court is expected to take about three weeks to deliver a verdict, a timetable which is likely to cloud Lithuania's entry into Nato on April 2 and might drag on to May 1, when the Baltic country becomes a member of the European Union.
The votes of 86 of the 141 members of parliament are needed to remove Paksas from office.
The scandal blew up at the end of October when a security services report accused Paksas and his office of shady links and parliament is awaiting the court's ruling before moving to a final vote.