BANGKOK—As it reaches the halfway point in its first term, signs have started to emerge that Thailand’s ruling party is losing some popularity. For the first time in 37 years, a candidate of the Democrat Party has won a parliamentary seat in Bangkok’s Don Muang constituency, a stronghold of the ruling Puea Thai (For Th ) party.
The Democrat eked out only a narrow win in Sunday’s by-election, but it’s having a major impact on Puea Thai—another in a growing list of problems.
Puea Thai, which beat the then-ruling Democrats in the general elections in July 2011, is under fire over a program in which the government buys rice from farmers at an above-market price. Prime Minister Yingluck Shinawatra and her ministers have repeatedly denied that the program has shown a loss of 260 billion baht ($8.5 billion)—a figure leaked to local media—but have failed to offer a figure of their own.
Puea Thai critics said Ms. Yingluck is trying to mimic populist policies of her brother, former Prime Minister Thaksin Shinawatra—perhaps the most popular but also most controversial figure in modern Thai politics. Mr. Thaksin was ousted by a military coup in 2006 and fled the country to avoid imprisonment on corruption charges that he continues to deny.
Earlier this year, the Yingluck administration sparked intense public scrutiny and raised concerns about corruption and the country’s fiscal position’s with a bill to borrow two trillion baht ($65.4 billion) to invest in high-speed trains, ports and other infrastructure projects.
The borrowing and the rice-pledging controversy have provided fresh fuel for long-simmering anti-Thaksin sentiments, prompting protests by Thais wearing stylized white Guy Fawkes masks like those seen in the film “V for Vendetta.” Calling itself V for Thailand, the movement was started by a former senator close to the anti-Thaksin “Yellow Shirts” and a retired police general who served as an aide to King Bhumibhol Adulyadej.
On Sunday, more than a thousand protesters, mostly middle-class—they frequently pulled out iPhones and iPads to record the event—rallied in downtown Bangkok to denounce Ms. Yingluck as a proxy for her brother. They chanted “Shinawatra, get out” and called the police “lackeys of Thaksin.”
Some protesters complained about a cost of living they said has skyrocketed since Ms. Yingluck approved a minimum-wage increase in Bangkok and other metropolitan cities. Some even called for a military coup to uproot the Shinawatras.
The white-mask protests are spreading from Bangkok to other Thai provinces, with the help of social media, online forums and cable TV. It may not gain a significant public support like its Yellow Shirt and pro-Thaksin Red Shirt predecessors, but polls and public sentiments show growing disenchantment with the Puea Thai government.
Mr. Thaksin on Monday could only urge his sister to release the loss figures from the rice program and act fast to stem public mistrust.
By Warangkana Chomchuen, Wilawan Watcharasakwet contributed to this article