Turkey's parliament reconvened on Monday with four former ministers of beleaguered Prime Minister Recep Tayyip Erdogan expected to defend themselves against corruption allegations.
The main opposition Republican People's Party (CHP) demanded the debate, once postponed, over a scandal that has spiralled into the most serious challenge yet to Erdogan's 11 years in power.
The interior, environment and economy ministers stepped down in December after police rounded up their sons on charges of bribery for construction projects and illicit money transfers to neighbouring Iran.
And in a major cabinet reshuffle, also in December, Erdogan replaced Turkey's EU affairs minister Egemen Bagis, who was also implicated.
All suspects in the probe are free pending a trial.
The four ministers are expected to defend themselves to the MPs on Monday in their first public appearance since the scandal erupted, a parliamentary source told AFP.
Although the session will not be televised, it will be streamed live on the parliament's website.
The assembly is also expected to debate whether the four should be investigated by separate commissions, as demanded by the CHP, or a single body, as demanded by the ruling Justice and Development Party (AKP).
The AKP, with 313 seats in the 550-member parliament, is expected to prevail, but the voting session is likely to continue past midnight.
The investigation is scheduled to start in mid-May, but its work will be interrupted by parliament's July recess in the run-up to a presidential election in August.
Erdogan, who is expected to stand in the election -- the first direct poll for Turkey's head of state -- has also been implicated in the corruption scandal through leaked audiotapes in which he can allegedly be heard talking to his son about hiding large sums of money.
The premier has accused followers of ally-turned-foe Fethullah Gulen, a Muslim preacher who lives in self-imposed exile in the United States, of concocting the graft scandal and spreading leaks in social media to topple the government.
Despite the allegations, Erdogan's AKP scored a crushing victory in the local polls, boosting the premier's ambitions for the presidency.