Voters in Georgia are voting in a parliamentary election regarded as President Mikhail Saakashvili's biggest test since he came to power in 2003.
Opposition leader Bidzina Ivanishvili, Georgia's richest man, accuses the president of acting undemocratically and trampling on people's rights.
Mr Saakashvili says his opponent will allow Russia to dominate the former Soviet republic.
The president led the country in a short war with Russia in 2008.
He has sought to portray the election as a choice between his progressive Western-leaning government, and a future dominated by Russia.
"Tomorrow, our enemy has its last chance to turn us off our path of independence," Mr Saakashvili said in a recorded address carried on state TV on Sunday.
"But I am confident that tomorrow our freedom-loving nation will take the ultimate and decisive step towards liberation from the pincers of the conqueror and towards integration into the house of Europe."
The government's reputation has taken a battering in recent weeks because of a prisoner-abuse scandal.
Videos broadcast on national television showed prison inmates being beaten and sexually abused by guards.
The scandal sparked street protests and has allowed Mr Ivanishvili to portray the government has high-handed and uncaring.
"This regime cannot be the leadership of our country. This system should collapse," he told supporters of his Georgian Dream coalition at a rally on Saturday.
Analysts say the election is crucial because the country's political system is being altered to give more power to parliament.
Mr Saakashvili's second term as president ends next year, and he is constitutionally barred from standing again.
So a parliamentary majority for his United National Movement could see him continue his domination of Georgian politics after he steps down.
The BBC's Damien McGuinness in Tbilisi says fist-fights are already a common feature of campaign meetings, and there are fears a dispute over the results could lead to violence.