The party now holds 71 of the chamber's 101 seats.
Kirill Koktysh, an analyst with the Moscow Institute of International Relations, says Voronin's party may lose some support but points out there are few strong rivals to challenge it.
(INSERT AUDIO -- Koktysh in Russian -- NC030432)
"[Voronin] has a good chance to stay in power simply because his success depends on the ability of the society to mobilize protests [and the society is not able to do this]," Koktysh says.
Opinion polls give the Communists about 50 percent of the vote, with each of the two biggest opposition parties -- the Democratic Moldova bloc and the People's Christian Democrats -- holding about 15 percent each. The barrier for entering parliament is 6 percent of the vote, and higher for blocs of two or more parties.
To become president, a candidate must win at least 60 percent of the vote in parliament. It's not certain that any party will be able to garner enough support to ensure their candidate victory in the first round.
It's also unclear what a victory for the Communists might mean in terms of the country's foreign policy.
The Communists won in 2001 on a promise to raise living standards, and Voronin also promised to improve ties with Moscow.
But in 2003 he broke with Moscow over the issue of Transdniester, accusing Russia of trying to prolong the breakaway conflict. Voronin has since embraced the idea of closer links with the European Union.
Koktysh says Voronin is walking what he calls a "zig-zag" line between Russia and the EU, and currently lacks strong support in either Moscow or Brussels.
The opposition says it is hoping for an Orange Revolution, similar to what happened recently in neighboring Ukraine. One of the parties, the Christian Democrats, has adopted orange as its party color, with the other main opposition party choosing yellow.
Voronin in recent days has appeared to try to diminish this possibility by casting himself in the role of reformer. In the past week, he's traveled to Kyiv to meet with new Ukrainian president Viktor Yushchenko and received visiting Georgian president Mikheil Saakashvili, leader of Georgia's Rose Revolution.
Reports say the Kremlin might be backing one of the opposition parties, the Democratic Moldova bloc led by Serafim Urechean.
The opposition has accused the Communists of using all means to stick to power. Urechean said recently the authorities "are unscrupulously using administrative resources and the state media" to promote the ruling party.
The Christian Democrats have already secured official permission to organize "meetings with the electorate" in the capital Chisinau for two weeks after polling day. However, Koktysh says he does not believe that the opposition parties can seriously challenge the political system.
He says the opposition has failed to coordinate it actions and mentioned some reasons for its lack of unity.
"It might have been possible [for the opposition] to unite if Voronin was such a dictator as [Alyaksandr] Lukashenka but this isn't the case. It was also possible to unite in the name of some future vision of Moldova, but in this case you need an industrial society [not an agrarian one as in Moldova]," Koktysh says.
The election is being watched closely in the West -- not just for who wins but how the vote is conducted.
U.S. Senator John McCain (Republican, Arizona) said in the interview with RFE/RL's Moldova service that fraudulent elections in Moldova would be viewed negatively.
"I think from the United States you would hear condemnation and criticism, and of course the United States and the Europeans would consider whatever options there are like resolutions and all that," McCain said.
U.S. President George W. Bush recently urged Moldovans to run a clean vote. Speaking in Bratislava, he said, "Moldova has the opportunity to place its democratic credentials beyond doubt."