Tens of thousands of Thais, wearing yellow hats and bandanas, rallied at a Bangkok fairground late Sunday chanting for Prime Minister Thaksin Shinawatra to leave office.
It was the third mass demonstration in as many weeks, and by far the largest against the prime minister one year after he was re-elected by a landslide.
Thaksin has been facing a rising tide of criticism since the controversial sale last month of stock shares in a company he founded.
The prime minister, responding to the pressure, Friday announced that he was dissolving parliament and calling elections in five weeks.
Mr. Thaksin says the election on the second of April will be important for the country, an election where people will decide, which system they want. He says he will accept the people's decision, and urges them to vote.
The embattled prime minister hoped to appease his critics and continue in power.
But many critics, including the three main opposition parties, say they may boycott the elections. Their leaders met and called for a meeting with the prime minister to discuss political reforms, including changes to the constitution.
They say that the prime minister's party controls three-fourths of parliament seats, the election commission, and most local governments in the country. And there is not enough time to organize their campaigns.
As a result, they say, the snap elections will only serve the prime minister's interests and will not address the corruption and abuse of office, which are undermining the country.
A professor at Bangkok's Chulalongkorn University, Thitinan Pongsuthirak, says positions have hardened between Mr. Thaksin and the coalition of academics, unions and civic groups that seek his resignation.
"The coalition now is bent on ousting Thaksin at all costs. Dissolving the house is not enough for them now. So, it puts an uncertainty into Thai politics. We have a growing uncertainty and growing likelihood of confrontation," said Thitinan Pongsuthirak.
Critics say Mr. Thaksin lost the moral authority to govern after his family sold nearly $2 billion worth of shares in the company he founded to a foreign investor, without paying any taxes. The tax-free sale was legal, but it angered many Thais. Critics say the sale also placed in foreign hands strategic assets, such as satellite and telecommunications licenses.