The Czech Republic's centre-right minority government has lost a vote of no-confidence midway through the country's six-month EU presidency.
Four rebel MPs voted with the opposition Social Democrats and Communists against PM Mirek Topolanek.
Mr Topolanek said he would step down, but correspondents say it is unclear how long he will remain in the post.
The European Commission said it was confident the Czech Republic could continue its EU role effectively.
Social Democrat leader Jiri Paroubek said ahead of the vote that the government could "complete the Czech EU presidency or its substantial part".
However, Mr Topolanek has ruled out the idea of a caretaker government until June, when the EU presidency passes to Sweden.
According to the constitution, Czech President Vaclav Klaus must decide who to choose to form a new administration. If three attempts to do so fail, early elections will be called.
Tuesday's no-confidence vote in the lower house followed accusations that one of Mr Topolanek's advisers had attempted to pressure the country's public TV channel into dropping a programme critical of a former Social Democratic MP who had decided to back the coalition.
It was passed by a majority of one vote after four former members of Mr Topolanek's minority coalition, who had become independents, sided with the opposition.
Together they garnered 101 votes in the 200-seat chamber, the minimum required.
"The government got what it deserved," Mr Paroubek said afterwards.
The BBC's Rob Cameron in Prague says this surprise result, which threw observers completely off guard, could have far-reaching consequences beyond the country's borders.
In addition to chairing the European Council, the Czech Republic is also in the middle of ratifying the Lisbon Treaty and is in talks with the United States on placing a radar base on Czech soil.
All these important foreign policy initiatives are now thrown into doubt, our correspondent adds.
After losing the vote, Mr Topolanek said he believed the country's position in Europe would inevitably be weakened.
"I believe it can complicate our negotiating power... partners in Europe have grown used to us negotiating hard," he told reporters.
However, the European Commission issued a statement expressing confidence that the Czech EU presidency would not be affected.
"The Commission has full trust that the national constitutional law allows for the Czech Republic to continue conducting the Council Presidency as effectively as it has done until now," it said.