Yingluck has until later on Monday to defend herself before the National Anti-Corruption Commission (NACC) against charges of dereliction of duty over a ruinously expensive rice-buying scheme.
If the commission recommends Yingluck's impeachment, and the Senate then seeks to remove her, it could be a tipping point for the pro-government "red shirts", who have mostly stayed out of the fray since anti-government protests first flared in November.
"We'll act when our democratically elected prime minister is kicked out by the elite," Suporn Attawong, a red shirt leader known by followers as "Rambo Isarn", told Reuters in Bangkok.
Leaders of the red shirt movement, formally called the United Front for Democracy against Dictatorship (UDD), say they are mustering recruits to be sent for military-style training in order to protect their own protesters if they go to the barricades.
Thailand's eight-year political crisis broadly pits the Bangkok elite and middle classes against the mostly rural supporters of Yingluck and her influential brother, Thaksin Shinawatra, who was ousted as premier by the military in 2006.
The red shirts have upped the ante in recent days, sealing off entrances to the national anti-corruption agency. Grenades were thrown at the offices of the agency one night late last week, but no one was injured.
There are fears that any march on Bangkok could end in a bloodbath similar to 2010 when red shirts camped out for weeks in the capital, demanding an early general election. That unrest ended with a military crackdown and at least 90 people died during the events, mostly Thaksin supporters.
Suporn says the UDD leadership will announce a plan of action on April 3. They tentatively expect to hold a rally on April 5, possibly in Bangkok, and to block a major highway connecting central Thailand to the northeast.
"If a major rally is held in Bangkok we will quickly mobilize our northeastern volunteers to act as super guards for red shirt protesters in the capital," said Suporn.
The red shirts have been trumpeting their readiness to use force to defend their prime mininister. But it is not always clear where the bluster ends and the real threats begin.
"I'm taking 1,000 people from 20 provinces in the northeast and sending them to camps where they will learn how to fight. Once that's in place, we're going to escalate our training and include more volunteers," Suporn said.
He wants to form a corps of bodyguards trained in martial arts to protect red shirt protesters. And he stressed that they would be unarmed, as stockpiling weapons would break the law.
The red shirts have begun to sound more militant under new leader Jatuporn Prompan, a straight-talker whose rise to the top post has been well received by the red shirt rank and file.
For all the fighting talk, the red shirts still appear to be at the recruitment stage, and camps have yet to be established.
Meantime, their opponents have waged a campaign of street protests in Bangkok over the past five months to destabilise Yingluck.
They want to install an unelected government that will push through electoral changes aimed at stopping Yingluck and Thaksin from gaining power again.
Despite his long absence from the country, Thaksin's supporters in the north and northeast remain fiercely loyal. They credit him with improving living standards in a region that was largely neglected before by the politicians in the capital.
In the northeastern city of Khon Kaen, a red shirt stronghold, pro-Thaksin activists are gearing up for a fight if Yingluck is removed by the army or the courts, the latter looking increasingly likely.
"People are saying in discussion forums on the radio station that they are willing to die for the cause," said Phuttiphong Khamhaengphon, a red shirt leader in Khon Kaen who is also a disc jockey at the Esan Record radio station.
If the anti-corruption commission recommends her impeachment, she could be removed from office by the upper house Senate, which held an election for half its members on Sunday. The anti-Thaksin camp would need a three-fifths majority to remove her.
Phuttiphong believes the crisis could deteriorate into open fighting in the coming months.
He said he had signed up 2,000 "strong men with good health" in Khon Kaen to protect red shirt activists. But his group, which he likens to a volunteer security force, has not yet undergone training either.
Seven years after staging the coup that removed Thaksin, Thailand's armed forces are also standing back. Army chief Prayuth Chan-ocha has repeatedly dismissed speculation the army will intervene in the crisis, aware that a military takeover could spark civil conflict.
But that hasn't stopped the army from threatening to shut down red shirt training camps.
"If the red shirts set up an army and are found to have weapons, we can't sit by idly and watch. We will have to act accordingly," army spokesman Winthai Suvaree told Reuters.