Romanian prosecutors have questioned Prime Minister Victor Ponta, who is suspected of forgery, tax evasion and money laundering.
The case, concerning Mr Ponta's work as a lawyer in 2007-2008, is being handled by the anti-corruption agency DNA.
President Klaus Iohannis has urged Mr Ponta to resign, saying it was "an impossible situation for Romania".
But Mr Ponta, who denies any wrongdoing, said only parliament can dismiss him.
He is accused of using forged invoices from a law firm, Sova and Associates, to buy two luxury apartments and a Mitsubishi Lancer car, Romanian media report.
The president, a centre-right politician, cannot suspend Mr Ponta without the approval of parliament, where Mr Ponta's centre-left Social Democratic Party (PSD) and its allies have a majority.
The PSD emerged out of the old Communist Party and Mr Ponta took office in 2012.
Threat of dismissal
The DNA has arrested several well-known figures in recent months, with former government ministers, media moguls, judges and prosecutors all under investigation.
They include Elena Udrea, a former minister of tourism and former presidential candidate.
The DNA investigation has also spread to Mr Ponta's mother, sister, brother-in-law Iulian Hertanu and senator Ilie Sarbu, who is his father-in-law.
After speaking to the president on Friday, Mr Ponta said: "I respect his public position but I was appointed in the job by Romania's parliament and only parliament can dismiss me."
Romania's constitution says parliament and the president can demand that legal proceedings be taken against government members.
Mr Ponta was an associate at the law firm of senator and former minister Dan Sova from 2007 to 2008.
Romania's tax office accuses the firm of defrauding Rovinari and Turceni power stations - for which it was providing legal services - of millions of euros.