Romania's parliament suspended President Traian Basescu ruling he had overstepped his powers.
This move sets the stage for an impeachment referendum.
In a vote that tightened the leftist government's grip on power, 256 of the bicameral parliament's 372 deputies that were present voted to suspend Basescu.
The vote was part of a wider political row that has paralysed lawmaking.
It also has raised doubts about Romania's ability to stick to its €5bn International Monetary Fund-led aid deal, hurting asset values.
The president is in charge of the country's foreign policy and nominates the prime minister.
Although the role is in part ceremonial, Basescu was able to influence the previous government's austerity policies.
It is suggested that he had close links to the centre-right Democrat-Liberal Party (PDL), which led that government.
Antonescu, whose party initiated today's vote, will now serve as president during Basescu's 30-day suspension until a referendum decides if he is to be impeached.
The political instability has sparked concerns in the EU, which Romania joined in 2007, about the future of EU-driven justice reforms and Romania's fight against graft.
The Commission has demanded Romania respect the rule of law and the independence of the judiciary.
Prime Minister Victor Ponta will travel to Brussels next week for talks with Comission President Barroso.
Ponta's government took office in May and has taken a series of measures to broaden its power in what is the EU's second-poorest country and one that is also in deep recession.