Thailand's anti-graft panel said Tuesday it would press charges against hundreds of politicians, mostly from the party of embattled Prime Minister Yingluck Shinawatra, over a failed attempt to amend the constitution.
The ruling adds to the political uncertainty in the kingdom, where the main opposition party is boycotting February elections called by Yingluck in an unsuccessful attempt to end weeks of mass anti-government protests.
The National Anti-Corruption Commission (NACC) -- whose mandate includes investigating possible abuse of power -- cleared 73 politicians including Yingluck of wrongdoing in connection with a bid to make the senate, the legislature's upper house, fully elected.
But 308 others from the upper and lower houses were found to have violated the law, based on a preliminary investigation, by drafting or proposing changes to the charter, panel spokesman Vicha Mahakun told reporters.
If officially found guilty by the commission their cases will be sent to the upper house of parliament, which has the power to ban them from politics for five years.
Yingluck's supporters see the case as one of a number of political manoeuvres aimed at removing her Puea Thai party from power.
Protesters seeking to curb the political dominance of the premier's billionaire family have vowed to block the February 2 election. They have the support of many in the kingdom's elite.
The demonstrators want an unelected "people's council" to run the country to oversee vague reforms, such as an end to alleged "vote buying" through populist policies, before new elections are held.
The anti-government movement is threatening to "shut down" Bangkok from January 13, with measures including setting up protest stages around the capital and cutting off power and water to government buildings.
They held a second "warm-up" march on Tuesday with thousands marching through the capital's riverside districts.
Security officials said Tuesday that Yingluck was ready to declare a state of emergency if needed next week.
"Everything has been prepared to declare emergency rule if the protests seem likely to escalate into violence, for example with attacks on people, buildings or acts of terrorism," National Security Council chief Paradorn Pattanatabut told reporters.
"Soldiers would be deployed at public buildings while police would act as fast response units and on the frontline," he said.
Thailand has been periodically convulsed by political bloodshed since Yingluck's older brother Thaksin Shinawatra was overthrown by royalist generals in a coup in 2006.
Eight people have been killed and about 400 wounded in recent street violence.
Legal rulings have played an important role in politically turbulent Thailand in the past, and Yingluck's opponents fear her party could fall victim to another judicial or military coup.
The attempt to reform the senate would have returned it to its pre-coup structure -- -- something observers say the establishment wants to avoid in order to limit Thaksin's electoral dominance.
Puea Thai deputy spokesman Anusorn Iamsa-ard said those charged were only doing their duty.
"They were MPs and their job was to issue laws," he said, adding that most of the lawmakers under investigation were planning to run in the upcoming election.
Yingluck's government still enjoys strong support in the north and northeast of the country and is expected to win the polls if they go ahead.
Adding to the uncertainty, the army chief has refused to rule out launching another coup.
But Thaksin's "Red Shirt" supporters have warned of a possible uprising if the military intervenes again.
"Once a coup takes place Red Shirts and all democracy-loving people will retaliate and Thailand will not be the same again," Red Shirt leader Jatuporn Prompan said Tuesday.
The recent civil strife is the worst since 2010, when more than 90 people were killed in a bloody military crackdown on pro-Thaksin Red Shirt protests under the previous government.
Ex-deputy premier Suthep Thaugsuban, who is leading the current protests, is due in court Wednesday to face a murder indictment over those deaths but it is unclear if he will attend.