Turkey's foreign Minister Abdullah Gul failed to win enough support in the first round of voting today to become the next president.
The main opposition party increased tensions by seeking to have the vote annulled.
The secularist CHP's demand highlights deep divisions between Turkey's secular elite, including army generals and judges as well as opposition parties, and the Islamist-rooted ruling AK Party of prime minister Tayyip Erdogan.
Secularists fear the election of the AK Party's Mr Gul would threaten Turkey's secular system of government that separates religion and politics. In Turkey the president is elected by parliament.
As expected, Mr Gul, an ex-Islamist, failed to secure enough support from deputies to win today's first round of voting, winning 357 votes, short of the required 367. A second round of voting is scheduled for next Wednesday.
The CHP asked the Constitutional Court to rule the vote invalid because there were fewer than two thirds, or 367 deputies, in the chamber at the time after opposition parties stayed away.
The court has said it will try to rule on the appeal before Wednesday. If it backs the opposition, Erdogan must call a snap general election. Outgoing president Ahmet Necdet Sezer would stay on as caretaker head of state until a new parliament could choose his successor.