Authorities in Thailand are bracing for another large rally Saturday, calling for the resignation of Prime Minister Thaksin Shinawatra, following a controversial stock sale and allegations of official corruption. The rallies come one year after Mr. Thaksin became the first prime minister in modern Thai history to be re-elected.

Thai Prime Minister Thaksin Shinawatra has moved quickly to bolster his political image after a mass anti-government rally last Saturday. He has made numerous public appearances and has received expressions of support from thousands of Thais.

The campaign follows a mass rally last week in Bangkok organized by media magnate Sondhi Limthongkul.

At the peak of the protest, Sondhi led demonstrators in chanting for the prime minister to "get out."

Mr. Thaksin, however, rejected the call.

He says his critics are only looking at snapshots, not the big picture, and that during his five years in office, he has made Thailand healthier on the economic, social and political fronts.

Criticism of the prime minister intensified after his family three weeks ago sold shares, to a Singaporean firm, in the corporation he founded. The family made nearly $2 billion in the deal, but incurred no taxes.

The tax-exempt sale was ruled legal, but many Thais were angered by the exemption for one of Thailand's wealthiest families. They also objected to the fact that the sale included important national assets, such as satellite, mobile phone and airline licenses.

A professor at Bangkok's Chulanlongkorn University, Thitinan Pongsuthirak, says the deal united Mr. Thaksin's various critics.

"This is now a coalition to overthrow Thaksin that has been joined by all kinds of groups that have been disaffected with Thaksin for a long time," he said.

Mr. Thaksin was elected by a landslide five years ago promising to end poverty and boost social services.

However, Thailand's educated elite in recent years has voiced increasing concern that the billionaire tycoon was accumulating unrestrained power, which was fueling corruption and undermining checks and balances in the fledgling democracy.

A founder of the Corruption Watch website, former Chulalongkorn University professor Tortrakul Yomnak, says the website has received hundreds of allegations.

"It seems that in every case of government spending, almost 95, 99 percent have some irregularities, corruption. Some are very small, but some are a very high percentage," he said.

He said the bribes range as high as 40 percent in some projects.

These critics have been joined by single-issue groups that oppose government initiatives on free-trade, privatization and environmentally questionable infrastructure projects. This alliance is organizing Saturday's rally.

The critics say the government has muzzled the Thai news media in order to keep criticism from the public.

A member of the Campaign for Popular Media Reform, Supinya Klangnarong, notes that private news outlets have been bought out by government allies and lawsuits brought against government critics.

"This government uses legal actions against journalists, academics or activists, so it creates a chilling effect on the climate of their critics for a long time," he said.

Professor Thitinan of Chulalongkorn University notes that one year after Mr. Thaksin's landslide re-election, many voters now want a change. He calls this a classic dilemma for a developing democracy.

"We don't have a mature democracy and there's a danger here," he said. "We don't want to violate the rules too often."

He says a democracy cannot repeatedly remove an elected leader using methods outside the constitution and the law. He says these must be given time to become established.

Mr. Thaksin continues to enjoy popularity among many Thais, especially the rural poor, and his two-thirds bloc of the seats in parliament remains strong, at least for now.

As a result, observers say the prime minister could simply try to weather the storm of criticism, or he could seek to work with his critics to improve governance and the democratic process.

They say a hardening of positions on either side could lead to political confrontation, and an increasingly weakened government.