Grindeanu said anti-riot police officers and three protesters were injured Thursday when protests in the capital Bucharest turned violent.
"Unfortunately, a peaceful protest tonight turned into a violent one. I must start by saying that I respect the right of Romanians to protest," Grindeanu said on his Facebook page.
The protests, among the largest the country has seen since the fall of communism in 1989, began after Grindeanu passed the decree without the vote of Parliament on Tuesday.
The measure, set to take effect in a little over a week, will decriminalize corruption that causes damage worth less than about $48,000 US (200,000 Romanian leu.)
It also will halt all investigations for pending corruption offenses, will prevent further cases related to these offenses to be brought into justice and could free some officials who are in prison for corruption.
On Thursday Grindeanu said he would not repeal the decree.
Abuse of power?
High-ranking politicians stand to directly benefit from the new law.
Liviu Dragnea -- the president of the ruling Social Democrat Party, which introduced the measure -- is currently under investigation for abuse of power, having previously received a two-year suspended sentence for an elections offense.
Dragnea blamed an "'ongoing campaign of lies and disinformation" for the public outcry against the measure, according to CNN's Romanian affiliate ProTV.
Over 2,000 abuse of power cases are currently being investigated by anti-corruption prosecutors, according to Reuters.
Not all officials support the emergency decree.
President Klaus Iohannis brought a formal challenge to Romania's Constitutional Court on Thursday and described the law as "a legal constitutional conflict between the government and the judicial system and parliament" during a televised news conference.
A spokesperson for Romania's Constitutional Court said that other government officials have until February 7 to file on the decree. After receiving all arguments, the court will rule on the law's constitutionality within 20 days, a court spokesperson told Reuters.
Nationwide protests to continue
Nationwide protests over the decree are expected to continue into the weekend. In addition to Bucharest, protesters have demonstrated in 50 other cities since the reforms were announced. Locations include Timisoara, Cluj-Napoca, Iasi, Sibiu, Brasov, Arad, Galati, Craiova, Constanta and Alba-Iulia.
On Wednesday, European Commission President Jean-Claude Juncker said
: "The fight against corruption needs to be advanced, not undone."
The embassies of Belgium, Canada, France, Germany, Netherlands and the United States issued a joint statement warning that Romania's international reputation -- and the security of the region -- could be put at risk.
"This act, in contravention to the collective wisdom of the entire judicial and rule of law community, credible elements of civil society, and the demonstrated concerns of Romanian citizens over the past two weeks, can only undermine Romania's standing in the international community and risks damaging partnerships that are based on common values, inherent in the guiding principles of the EU and NATO," the statement said.