Yaowapa Wongsawat, the Pheu Thai Party candidate contesting the by-election in Chiang Mai's Constituency 3 tomorrow, is expected to win comfortably with at least 100,000 votes, a party source said.
As a sister of former prime minister Thaksin Shinawatra and current premier Yingluck Shinawatra, Ms Yaowapa is considered a clear favourite in the by-election in her native province, a Pheu Thai stronghold.
The by-election will be a battle between Ms Yaowapa and the Democrat candidate Kingkan Na Chiang Mai. Constituency 3 covers San Kamphaeng, Doi Saket and Mae On districts.
The source predicted Ms Yaowapa will have a relatively easy win in San Kamphaeng, her hometown, and Mae On, but Ms Kingkan, also a former MP of the province, is a favourite in Doi Saket. The constituency has about 130,000 eligible voters.
Ms Yaowapa feels the need to restore the pride of party MPs in the North and to boost the morale of 111 former executives of the dissolved Thai Rak Thai, the original incarnation of Pheu Thai. She was formerly deputy party leader of Thai Rak Thai and among the 111 banned executives. The ban expired last year.
The by-election follows the resignation of Pheu Thai's Kasem Nimmonrat, who cited health problems.
But political observers believed Pheu Thai was grooming Ms Yaowapa as a potential candidate for prime minister should Ms Yingluck be disqualified for any reason.
Mr Kasem ran in the by-election on June 2 last year for the seat vacated by Chinnicha Wongsawat, who was disqualified by the Supreme Court's Criminal Division for Holders of Political Positions after she was found to have falsely declared her assets and liabilities.
Ms Chinnicha is a daughter of Ms Yaowapa and former prime minister Somchai Wongsawat.
Mr Kasem garnered 72,385 votes in the Constituency 3 by-election on June 2, 2012, while Ms Chinnicha won 81,450 votes in the 2011 general election.
Pheu Thai believes Ms Yaowapa could win up to 100,000 votes on Sunday.
PM's Office Minister Varathep Rattanakorn, who helps campaign for Ms Yaowapa, said voters are now satisfied with Pheu Thai's performance.
Duantemduang Na Chiang Mai, Ms Kingkan's daughter, said the by-election has significant implications for Chiang Mai residents. It could prove Pheu Thai's populist policies are wrong as the government has failed to address problems faced by local people.
Ms Duantemduang believes Ms Kingkan will win despite her rival wielding influence over local officials and state control mechanisms.
Meanwhile, Democrat MP for Tak Thanitphol Chaiyanant, who is also the director of the party's election centre in the by-election, yesterday filed a complaint with the Chiang Mai election committee asking it to investigate alleged violations of election law.
Mr Thanitphol claimed that on Thursday night two men were seen in front of Ms Kingkan's house in Chiang Mai. The two men claimed to be police officers, he said.
Mr Thanitphol said the two men also carried pistols and mobile phones.
When he asked to see the mobile phones, he was shown messages from high-ranking police officers through the Line chat application.
Mr Thanitphol said the messages appeared to be in support of political parties, and had nothing to do with police work.
He then asked to copy the messages and filed complaints with police as well as the Election Commission.
He said the party was gathering evidence to take legal action against state officials who fail to maintain neutrality during the poll.