The head of Romania's ruling Social Democrat party was sentenced to three and a half years in prison by the Supreme Court on Thursday for inciting abuse of office.
Liviu Dragnea, who is also speaker of the lower house, has denied all the charges and is expected to appeal.
More than 5,000 people gathered outside government headquarters calling for the resignation of Dragnea as speaker as well as of the Prime Minister, Viorica Dancila.
Some also expressed anger at the leniency of the sentence.
A fresh criminal conviction for Dragnea, who is already barred from becoming prime minister because of a previous conviction for vote-rigging, could weaken his grip on Romania's
biggest party and the five-month-old government.