They accuse Yingluck's government of carrying on the practices of her billionaire brother Thaksin Shinawatra, a former prime minister they allege used the family fortune and state funds to influence voters and subvert democracy.
Thaksin was ousted in a military coup in 2006 after street protests accusing him of corruption and abuse of power.
The coup triggered a sometimes-violent and still active struggle for power between Thaksin's supporters and opponents.
He fled into exile in 2008 to avoid a two-year prison sentence for a conflict of interest.
About 49 million of the nation's 64 million people are eligible to cast ballots in February, and 2.16 million applied for early voting.
But even before Sunday, there had been increasing doubt that the Feb. 2 poll would go ahead.
The Election Commission has argued the poll should be delayed because of concern over possible violence.
But critics accuse the commission, which is supposed to be a neutral body, of bias.
The commission pointedly failed to condemn an effort by protesters to disrupt candidate registration in December, and its chief has posed for at least one smiling photo with demonstrators.
Analysts say the courts and the country's independent oversight agencies all tilt heavily against the Shinawatras' political machine.
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