A total of 1.6 lakh voters are eligible to cast their ballots in the polls.
Though the main battle in Neyyatinkara, situated in the southernmost part of the state, is between R Selvaraj (Congress) and F Lawrence (CPI-M) of LDF, entry of former Union Minister and senior BJP leader O Rajagopal has virtually turned the contest into a three-cornered one.
The by-poll is especially crucial for the CPI-M as it is their sitting seat, vacated by R Selvaraj, who has joined the Congress and is now contesting on the `hand' symbol.
The poll also comes at a time when the CPIM is facing flak over the `politics of violence' allegedly perpetrated by them, as several party activists had been arrested in connection with the murder of RMP leader T P Chandrasekharan at Onchiyam in Kozhikode on May 4.
The party had lost the recent bypoll at Piravom where UDF candidate Anoop Jacob won by a huge majority and restored the UDF's tally to 72 in the 140-member assembly. Only a win for LDF in Neyyattinkara will enable them to retain their number in the assembly at 68, which they secured in the 2011 polls.
While the CPI-M used the `traitor' tag against Selvaraj and the rising prices during its campaign, the UDF highlighted the the achievements of the one-year rule of the Oommen Chandy Government.
UDF also seized on the recent outburst of CPI-M district secretary M M Mani that his party had killed its political rivals to intensify its campaign against `murder politics.'
Neyyatinkara has a total electorate of 1,64,970. Selvaraj won the seat in 2011 with a margin of over 6,000 votes defeating his nearest Congress rival Thampanoor Ravi, who had won the seat in 1991, 1996 and 2006.