That could lead to confrontation with anti-government protest groups in the capital, Bangkok that have for six months been trying to topple Yingluck. Demonstrations disrupted a general election in February she had been expected to win.
The crisis broadly pits Bangkok's middle class and royalist establishment against the poor, rural supporters of Yingluck and her brother, ex-premier Thaksin Shinawatra, ousted by the military in 2006 and now living in exile to avoid a jail term handed down in 2008 for abuse of power.
Yingluck's supporters accuse the court of bias in frequently ruling against the government.
In 2008, the court forced two Thaksin-linked prime ministers from office. A similar ruling against Yingluck is expected today.
Yingluck defended herself in court yesterday against a charge relating to her transfer of National Security Council chief Thawil Pliensri in 2011, which opponents say was designed to benefit her Puea Thai Party and a family member.
Yingluck, looking composed as she took the stand in a blue silk suit, said a committee of ministers had made the decision to transfer the security chief.
"I did not interfere in the decision process ... which should be for the benefit of the land," Yingluck told the court. "I have never benefited from any transfer of civil servants."
Some legal experts say her entire government will have to go if she is forced to step down. Her party rejects that.
She has led a caretaker administration with limited powers since dissolving parliament in December ahead of the election. Her party says another interim prime minister can be chosen from her five deputies.
"There is no reason why the whole cabinet should go with her," Noppadon Pattama, a legal adviser to Thaksin said. "That would be like a double execution."