Prime Minister Viorica Dancila has 45 days to ask for a confidence vote. Meanwhile, the main opposition Liberal Party said it planned to launch a no-confidence vote against the government next month.

Junior coalition party ALDE withdrew from government on Monday, two days after its leader Calin Popescu Tariceanu lost a bid to become the sole pro-government candidate in a presidential election scheduled for November.

The Social Democrats (PSD) instead picked Dancila to challenge incumbent Iohannis.

The PSD is now 25 votes short of a majority and will try to negotiate support with other parties.

"If the new government structure will not be approved, I assure Romanians that there are correct, democratic and constitutional solutions to keep Romania from a deep crisis," Iohannis said, adding the government was "toxic" for its attempts to weaken anti-corruption laws and economic policies.

"There are sufficient votes in parliament to support even a transition solution, one that will replace the current government. All opposition parties must be reasonable in case of a crisis."

Analysts said opposition parties would be reluctant to form a new government for a year, as they could lose popular support ahead of next year's election.

Early polls cannot legally be triggered six months before a presidential election, opening the way for prolonged uncertainty and stalled policymaking.

EU and US officials have strongly criticised the governing alliance for an overhaul of Romania's judiciary that they see as a threat to the rule of law, and for watering down anti-graft legislation. Expansionary fiscal and wage policies have increased the country's budget and current account deficits.

The Romanian leu held stable on Wednesday but is down 1.6 percent this year.

"We will try to obtain the necessary support to finish our term," Dancila told reporters late on Wednesday. "Not because we are clinging to our seats, but because we have a responsibility towards Romanians."

Voters turned on the government in European parliament elections in May, with the PSD's support almost halving while ALDE was unable to reach the threshold to enter the assembly.