Turkey's chief prosecutor has asked the Constitutional Court to ban the governing AK Party, accusing it of anti-secular activities.
The AKP won 47% in last year's general elections
Abdurrahman Yalcinkaya said he believed that there was enough evidence to show the party had been contravening Turkey's secular constitution.
The AK Party, which has Islamist roots, won last year's general elections.
So any move to close it will be extremely controversial, the BBC's Sarah Rainsford in Istanbul says.
The AKP is already locked in a battle with Turkey's secular elite, backed by the powerful military, over recent changes on the headscarf issue.
The Constitutional Court is reviewing an appeal by the main pro-secular opposition party on the validity of parliament's constitutional amendments in February to allow women wear Islamic headscarves at universities.
The scarf reform has prompted major controversy in Turkey
The AKP has argued that the headscarf ban unfairly bars large numbers of girls from higher education in a nation where about 66% of women wear the scarf.
Many secularists in the country equate the wearing of the headscarf with political Islam.
In a surprise announcement, Mr Yalcinkaya, the chief prosecutor at the Court of Appeals, said he had filed a court request for the closure of the AKP.
He also revealed that the party had been under investigation for six months.
Speaking on Turkish television later on Friday, an AKP lawmaker said he was shocked at the news.
The lawmaker said that senior party officials and lawyers were now holding an emergency meeting in the capital Ankara.
The AKP has its roots in an Islamist party that has been banned.
But the government of Prime Minister Recep Tayyip Erdogan - which is negotiating for Turkey to join the EU - has always insisted that its political views have changed.