
The race is billed as the proxy battle by the brothers from two prominent families.
The by-election, scheduled for August 30, is to fill the House seat vacated by Deputy Prime Minister Suthep Thuagsuban who voluntarily resigned following his involvement in the share-holding case.
Pending the official endorsement by the Democrat Party, Suthep has named his brother Thanee Thuagsuban as his successor.
The Thuagsubans and the Wichaidits both are political families, each claiming the southern province as stronghold.
The main opposition party has appointed Yingluck Shinawatra, younger sister of ex-premier Thaksin Shinawatra, as the campaign manager.