Democrat Party leader Abhisit Vejjajiva on Sunday urged citizens to vote, saying a clear mandate for a party to run the country would keep the Senate at bay.
Voters should use the election to "send a clear signal about which party they want to administer the country," the former prime minister said during a launch of campaigns in Bangkok.
"Their voices must be loud enough for the 250 senators not directly elected by the people to respect," he added.
Mr Abhisit warned that attempts to form a government against the will of voters would reignite political conflicts. He remained confident that the poll will be held by the deadline of May 9 as mapped out in the timeline.
The Democrat Party and its arch rival, Pheu Thai Party, will face a formidable newcomer, Phalang Pracharat Party (PRPP), set up to support Prayut Chan-o-cha to become prime minister after the election.
The National Council for Peace and Order, with Gen Prayut as chairman, will also handpick 250 senators to join the 500 MPs in the House of Representatives. The senators will join the elected lawmakers in selecting and voting for the candidates for prime minister after the election.
The PRPP is expected to offer Gen Prayut as a candidate for the premiership.
The Democrat Party is fielding candidates in all 30 constituencies in Bangkok, expected to be one of the fiercest battlegrounds for MP hopefuls in the election.
One of its more controversial candidate choices is former MP Huwaideeya Pitsuwan Useng, a younger sister of late Asean secretary-general Surin, who decided to move from her home turf in Nakhon Si Thammarat province to constituency 16 in the capital for the election.
The constituency -- covering Klong Sam Wa district -- was previously dominated by Samai Charoenchang, a former Democrat MP who decided to take a break from politics to concentrate on Islamic affairs. He is believed to have supported Natthanan Kalayasiri to replace him, but the party opted for Ms Huwaideeya instead.
Mr Samai has not yet to clarify whether he will use his political influence to back Ms Huwaideeya, but she is expecting his support.
"Deep inside, I still believe that he will not leave me alone," she told reporters on Wednesday.
