The demonstration came amid a deepening political crisis after two key government allies said Friday that the emergency government decree passed early Wednesday without input from parliament was not constitutional.
"The fight against corruption needs to be advanced, not undone".
Florin Jianu, Romania's minister of business, trade and entrepreneurship, has resigned from the cabinet over the decree.
It is the "ethical thing to do", he said, "not for my professional honesty, my conscience is clean on that front, but for my child".
"How am I going to look him in the eye and what am I going to tell him over the years?" he wrote. Social Democratic leader Liviu Dragnea is serving a two-year suspended sentence for electoral fraud and faces another abuse-of-office probe in which he denies wrongdoing.
President Klaus Iohannis took part in an emergency meeting of the CSM, telling reporters afterwards: "The problem is that one can not act the way the government did in a country with the rule of law, which Romania is and wants to remain". The court has yet to say when it will consider the challenge.
Ombudsman Victor Ciorbea, who previously backed the government's ordinance, reversed his position Friday, and said he would tell the Constitutional Court that the decree to decriminalize official misconduct under a certain dollar amount was "not justified".
Marine Le Pen refuses to repay €300000 in 'misspent' European Union funds
Le Pen is known for her anti-Muslim, anti-immigrant positions and has won the endorsement and admiration of white supremacists. That agency has also taken the case against Le Pen to French courts, which will decide whether other sanctions are warranted.
The government says it is created to ease prison overcrowding and bring the criminal code into line with recent constitutional court rulings.
The National Anticorruption Directorate has prosecuted 1,170 cases of abuse in office during the past three years with damages worth 1 billion euros ($1.07 billion), just under one-third of all of its cases, she said.
The Social Democrats were driven from power by protests in late 2015 after a nightclub fire killed 64 people and triggered widespread anger over corruption and impunity when it emerged the venue lacked emergency exits and safety permits.
"The PSD won elections (in December) with a huge vote".
He urged the government of Prime Minister Sorin Grindeanu to annul the controversial decree.
These events have resulted in major protests all throughout Romania and in the President of the EU Commission, Jean-Claude Juncker, and First Vice President, Frans Timmermans, releasing a joint statement today, saying that the Commission is "following the latest developments in Romania with great concern". Despite the pressure exerted by civil society, embassies of Western democracies, European Union leaders and institutions, and even a few PSD and ALDE members who resigned or declared themselves against the ordinance, the government proves the stubbornness of a dictatorship.