The announcement by the Constitutional Court came amid criticism from Yingluck supporters that the courts are trying to topple the prime minister through unfair use of the legal system after four months of anti-government protests have failed to unseat her.
The latest case was lodged by anti-government senators who say Yingluck violated the constitution by transferring her National Security Council chief in 2011 to another position. In February, another court ruled the official, Thawil Pliensri, must be restored to his job.
Thailand has been gripped by political conflict since 2006, when then-Prime Minister Thaksin Shinawatra, Yingluck's brother, was ousted in a military coup after being accused of corruption and abuse of power.
Thaksin's supporters and opponents have taken to the streets for extended periods in a power struggle that is currently focused on removing Yingluck, who took office in 2011. Opponents say she is a proxy for her brother, who is living overseas in self-imposed exile.
Currently, Yingluck is a caretaker prime minister, having called early elections in February as a way of affirming her mandate after the protests against her began. However, the Feb. 2 polls were annulled last month by the Constitutional Court and no date has been set for a new election.
Several other legal cases are pending against members of her party that could make it impossible for her to form a government.
