A day after more than 50,000 red-shirted protesters occupied an intersection of sleek upmarket department stores and five-star hotels, the government warned they could face up to a year in jail and a 20,000 baht ($620) fine each if they stay.
The gathering also violated a tough Internal Security Act imposed last month, said the Center for Administration of Peace and Order, a special government body set up during the protests.
"The way the rally is being held is inappropriate and unlawful," Prime Minister Abhisit Vejjajiva said after failed talks between authorities and the protesters.
The protesters ignored two deadlines to leave the area where Central World , the second-largest shopping complex in Southeast Asia, and half a dozen other big malls and retailers shut their doors for a second day in response to the rally.
But there was no sign security forces would disperse the mostly rural and working-class "red shirts", who say they will not leave until Abhisit dissolves parliament and calls elections.
"Abhisit will not dare" give an order to disperse the crowd, Jatuporn Prompan, a "red shirt" leader, said from a makeshift stage. "If bullets are fired, it will be a disaster for him."
Another protest leader, Veera Musikapong, said they would remain until Monday at least. "This area is a symbol of the Bangkok elite," he said. "We want to show them they cannot rule without the consensus of the people."
Backed by Thailand's powerful military and royalist establishment, Abhisit said a peaceful poll now would be difficult given the tensions and repeated his recent offer to dissolve parliament in December, a year early.
"Opposing political opinions remain so widely different they do not create an atmosphere for a peaceful and orderly election, one that can ease and resolve the rift in society," he said.
The British-born, Oxford-educated economist urged Bangkok's 15 million people to show restraint amid signs of frustration, underscored by a counter-rally on Friday by "pink shirt" protesters who say the "red shirts" are unreasonable.
Analysts say Abhisit would likely lose an election if it were held now, raising investment risks in Southeast Asia's second-biggest economy following a $1.6 billion surge of foreign investment in Thai stocks over the past five weeks on expectations he would survive the showdown.
Economists also caution continued political turmoil could force the central bank to delay an expected interest-rate rise.
The "red shirts", supporters of twice-elected and now fugitive former prime minister Thaksin Shinawatra, say Abhisit has no popular mandate and came to power illegitimately, heading a coalition the military cobbled together after courts dissolved a pro-Thaksin party that led the previous government.
Abhisit says he was voted into office by the same parliament that picked his Thaksin-allied predecessors.
In 2008, yellow-shirted protesters who opposed Thaksin's allies in the previous government occupied the prime minister's office for three months and then blockaded Bangkok's main airport until a court expelled the government.
At the centre of the impasse is Thaksin, a former telecoms tycoon seen as authoritarian and corrupt before he was ousted in a 2006 coup but a rallying symbol for the poor as the first Thai civilian leader to reach out to rural voters.
The occupation of one Bangkok's biggest commercial districts has stoked concerns about a rippling impact on tourism and the economy ahead of Thailand's April 13-15 Songkran holidays.
"We have nothing against peaceful democratic protests, but this has affected the normal way of life," said Apichart Singka-aree, director and former president of the private Association of Thai Travel Agents.
"Out of some 100 previously booked flights for Chinese tourists to fly in for the Songkran festival, over 60 have been cancelled. We are trying to save the remaining 30 something flights," he told Reuters.
