"We are concerned by the speed and consequences of decisions taken over the last few weeks," said EU spokeswoman Pia Ahrenkilde Hansen.
European Commission President Manuel Barroso has asked Romania's Prime Minister Victor Ponta to come to Brussels Thursday to discuss the country's political turmoil.
Last Friday, the parliament voted to impeach Basescu, accusing the president of having overstepped his authority. On Monday, the supreme court upheld that vote, setting the stage for a July 29 referendum on whether Basescu should be removed from office.
Both the EU and the United States say they are worried about democracy and due process in Romania. The country joined the EU in 2007, eight years after it emerged from communism.
Basescu, 60, and Ponta, 39, are locked in a power struggle. Basescu's opponents accused him of meddling in affairs that are the province of the prime minister, trying to influence judicial affairs and making bigoted remarks about Gypsies and disabled people.
Basescu has denied any wrongdoing.
"The elected president cannot be a mute," he said last week. "He has to assume responsibilities.
Basescu is a center-right politician but, as president, is banned from membership in any party.
Ponta heads the left-leaning Social Democratic Party. He became prime minister May 7, the third in four months. Unlike those who have held the post over the past decade, Ponta has not been deferential to the president but has moved instead to sideline Basescu allies.
Basescu was impeached in 2007 but survived a referendum.