Prosecutors say Victor Ponta is suspected of a conflict of interest, money laundering and tax evasion on June 5. He denies wrongdoing.
President Klaus Iohannis called on Ponta to resign as premier, and he refused.
The allegations stem from work that Ponta did as a lawyer in 2007 to 2008 when he was a lawmaker.
Ponta wrote on his Facebook page today that he was quitting the party leadership to prove his innocence. He is due to appear before anti-corruption prosecutors tomorrow.
