The head of Romania's ruling Social Democratic Party (PSD), Liviu Dragnea, has been jailed for corruption after his attempts to appeal an earlier conviction failed.
Romania's Supreme Court upheld on Monday a three-and-a-half year prison sentence against Dragnea.
The politician, 56, was found guilty last year of having two party members paid by a state agency for fake jobs.
The ruling came as his PSD suffered huge losses at the European elections.
Prosecutors said that by using his influence as a government official, Dragnea procured fake jobs at a child protection agency for two women working for his party.
The women admitted to working for the party while receiving salaries from the agency.
Dragnea, who denies any wrongdoing, appealed the initial verdict and was allowed to remain free.
In live footage on Romanian television on Monday, the powerful politician was seen being driven in a police car into the Rahova prison on the outskirts of Bucharest.
Dragnea is widely viewed as the most powerful figure in Romanian politics.
He was barred from becoming prime minister because of a 2016 conviction for vote-rigging.
But observers say he has still wielded power from behind the scenes, directing his PSD and the government they lead.
The politician was a key figure in the PSD's push for controversial judicial reforms, which have chipped away at the independence of the courts, sparking mass protests in Romania and clashes with the European Union.
The ruling on Monday came as Dragnea's PSD suffered major losses in the European election.
The party fell to second place, behind the opposition National Liberal party, gaining less than 23% of the vote.
Dragnea is also under investigation in a separate case for allegedly forming a criminal group to siphon off cash from state projects.
He has maintained his innocence in the cases against him, saying the charges are politically motivated.