"The president [Traian Basescu] succeeded in triggering a political crisis."
But Adriean Videanu, a Liberal Democrat economy minister, said the PSD was to blame for the crisis and called the party "hypocritical" for walking out.
The coalition's break up comes less than two months before a presidential election and, under Romanian law, no legislative votes can be held before a presidential poll.
The Democrat-Liberals, the remaining partners of the coalition, are able to rule alone for a few weeks, but their survival will depend on support from the opposition.
Economists have said the collapse could call into question Romania's ability to meet fiscal targets set by the International Monetary Fund in return for the $29bn aid package it led for the country this year.
"One needs to see how a minority government, if that's what we do get, can continue to adhere to the IMF programme. That's key," Koon Chow, a strategist at Barclays Capital, told the Reuters news agency.
"The worst that could happen is that the next tranche will be delayed for a few months, I don't think the next government will walk out of the programme," he said.
Romania is currently deep in recession, and dependent on an IMF loan to pay state sector salaries.
In recent weeks there have been protests and strikes by railway workers, magistrates and some public workers.