More than 18 million Romanians are eligible to vote, including about 2 million citizens living abroad who can vote in embassies and other locations.
A majority of those casting ballots would have to vote against Basescu for him to be removed from office. There is no threshold required for the vote to be valid.
Romanian broadcasting rules forbid politicians making comments that could influence the outcome of the election.
However, Mircea Geoana, who heads the opposition Social Democratic Party, which voted to suspend Basescu, told reporters: "I voted for the chance of a new beginning for all those who don't want scandal and chaos and who want to live in ... a democratic Europe ... We need a new president."The current political crisis started with an escalating conflict between Basescu and Prime Minister Calin Popescu Tariceanu, a former ally.
The two clashed on policy and attacked each other in the media. Last month, Tariceanu expelled several ministers from his Cabinet who were seen as being close to Basescu, including the reformist justice minister, Monica Macovei.
Basescu, who is known for his outspoken style, has also clashed with members of parliament, whom he accused of drafting laws for special interests.
Opponents, mostly ex-Communist Social Democrats who were tainted by corruption when they were in power for most of 1990s, accuse Basescu of using intelligence services to spy on opposition politicians.
Last month, five ruling and opposition parties ignored a court ruling that Basescu did not abuse his powers and voted in parliament to suspend Basescu, accusing him of violating the constitution.
Romanian law allows parliament to suspend the president, who has limited powers and cannot dissolve parliament or sack the prime minister.
The European Union, which Romania joined in January, has been watching nervously as the political disputes threaten to slow critical reforms such as fighting graft and making the justice system more efficient.
Adrian Cioroianu, the foreign minister, warned on Friday that Europe's patience with Romania "has a limit," and that after the referendum politicians should stop fighting and "get back to work."
Basescu says he will uphold a promise Romania made up joining the EU that it would crack down on endemic corruption.