Thailand's capital of Bangkok is in lockdown as tens of thousands of demonstrators prepare to converge for protests against Prime Minister Yingluck Shinawatra.
Authorities have deployed 17,000 police officers on the streets of the capital in fear of a repeat of demonstration violence that rocked the country for months two years ago.
Fears have been raised that the rally, led by retired army general Boonlert Kaewprasit, could turn violent and attempt to overturn the government.
"[Demonstrators] seek to overthrow an elected government and democratic rule and there is evidence that violence may be used to achieve those ends," Shinawatra said in a TV message to the nation.
She invoked a special security law that allows police to close roads, impose curfews and ban use of electronic devices in the area where the protest is to take place.
"Anytime you have tens of thousands of people converging and assembling in a central Bangkok location, it becomes a government stability concern," Thitinan Pongsudhirak, a political scientist at Bangkok's Chulalongkorn University, said.
Kaewprasit's royalist movement, Pitak Siam - Protect Thailand - is linked to the popular Yellow Shirt movement that toppled the government of Shinawatra's brother, Thaksin, in a military coup in 2006, and that of his successor, Samak Sundaravej, in 2008.
Thaksin Shinawatra, the former Manchester City owner, has lived in self-imposed exile in Dubai since 2008 following a conviction over corruption allegations.
Protesters accused his sister of authoritarianism and undermining the popular constitutional monarchy, a claim denied by her government.
She became prime minister in 2011 after violent demonstrations in 2010 - this time by her brother's supporters, the Red Shirts - forced the government to call early elections.
Ninety-one people died and 1,700 were injured in that violence as the military tried to clear protesters after a two-month occupation of central Bangkok.