Some Serbians are voting Wednesday in repeat elections after irregularities in the April 24 parliamentary polls.
Only 20,000 of the 6.7 million registered voters may take part in the repeat vote being held in 15 polling stations because of problems reported by both the opposition and the government.
However, the handful of voters will decide on 10 per cent of the 250 seats in parliament.
The April elections were called by conservative Prime Minister Aleksandar Vucic two years ahead of schedule.
The victory of the coalition grouped around Vucic's Progressive Party (SNS), which won 48.2 per cent of the votes, is not in question - but the number of the seats it will control is.
Vucic and the SNS go into Wednesday's vote with 138 of the 250 seats.
The Socialist Party (SPS) has 31 seats, the far-right Radical Party (SRS) 23, the reformist Enough (DJB) and the Democratic Party 17 each and former Serbian president Boris Tadic's bloc 14 seats.
But a seventh ticket, the extreme rightist movement Dveri, was in the provisional count a single vote short of reaching 5 per cent of the votes and taking 13 seats.
If, in the repeat election, Dveri win 5 per cent plus that one vote, it will take the 13 seats - seven from Vucic's tally, taking it down to 131 and six from the remaining five parties.
In that case, Vucic would drop to only six votes above the halfway mark of 125, dramatically lower than the 158 seats his bloc controlled in the previous parliament.
However, if Tadic's bloc also falls below the threshold along with Dveri, Vucic and the SNS would benefit the most and end up with around 145 seats.
Ethnic minority representatives control 10 seats in either case.
Results are expected shortly after voting ends at 8 pm (1800 GMT).