The protesters, who accuse Ms Yingluck of being the puppet of her self-exiled brother and former premier, Thaksin Shinawatra, want an appointed "people's council" to oversee a vague reform platform, which includes electoral reform, decentralising power, and a volunteer police force, over a 12-month period before any future election.
The crisis, an outbreak of turmoil stretching back eight years, began in November and has become a drag on the Thai economy. The baht slid on Friday to its lowest against the dollar since February 2010 and the .SETI stock index has lost 15% since November.
Ms Yingluck, her brother and their support base among the rural poor in the populous north and northeast are pitted against protesters who draw support from Bangkok's conservative, royalist elite and middle classes and the south.
Protest leader Suthep Thaugsuban, from the main opposition Democrat Party, said marches would be held on tomorrow and Thursday, leading up a "shutdown" on January 13.