Registrations for party candidates in the November 17 election opened yesterday with up to 130 sitting MPs expected to change allegiance.
The registrations, to close at the end of the week, have been keenly awaited by analysts as an indication of which way the election will swing.
It is forming as a close, two-horse race between traditional contender, former premier Chuan Leekpai's Democrats, and the party of military powerhouse General Chavalit Yongchaiyudh.
Defence Minister General Chavalit is expected to drag more than 60 sitting MPs from other parties into his New Aspiration Party - most of them from disgraced caretaker prime minister Banharn Silpa-archa's Chart Thai.
Before the election in July last year, the Democrat Party lost support after some of its members were implicated in a land-buying scandal and Mr Chuan was forced to dissolve Parliament.
Much of that lost support is set to return this election after a disastrous 14 months for the economy - showing the worst figures in a decade - under Mr Banharn.
Analysts say there are two keys as to who will form the next government - who can control seats in the country's volatile northeastern provinces and the allegiance of the third largest party led by another former premier, Chatichai Choon-havan.