More than 50,000 protesters defied orders to leave the Thai capital's main shopping district on Sunday, despite threats of mass arrests.
Despite repeated warnings they could face up to a year in jail, the Red Shirt protesters remained encamped for a second night at a major intersection lined by upmarket department stores and five-star hotels.
Deputy Prime Minister Suthep Thaugsuban said the government would seek a court order on Monday to end the rally, which he says violates a tough Internal Security Act imposed last month.
The protesters say they will not leave until parliament is dissolved and fresh elections are called.
They are already occupying two areas: the shopping district and Phan Fah Bridge in Bangkok's old quarter.
Prime Minister Abhisit Vejjajiva said a peaceful poll now would be difficult due to the tensions and repeated his recent offer to dissolve parliament in December, a year early.
The demonstrators are mainly supporters of former prime minister, Thaksin Shinawatra, who was ousted as prime minister of Thailand in a coup in 2006.
