Prolific petitioner and activist Srisuwan Janya has asked the National Anti-Corruption Commission to investigate Pannika Wanich, a Future Forward Party MP, over a controversial post she made on social media.
Earlier this week, Palang Pracharath MP Parina Kraikup accused Ms Pannika of making an inappropriate gesture to King Rama IX in a picture posted on her Facebook page.
The photo features her and her friends in graduation gowns back in 2010 gesturing toward a picture of the late monarch in manner deemed offensive by some.
In their swearing in ceremony, MPs take vow to respect and uphold the institution of the monarchy which is held in high esteem.
Mr Srisuwan, secretary-general of the Association to Protect the Thai Constitution, said the posts could constitute a breach of ethics and therefore provide the basis for an investigation.
"Although the posts and the photos appeared on Facebook a long time ago, they had not been deleted," Mr Srisuwan added.
His petition came a day after the police started an initial investigation into the affair.
Pol Lt Gen Piya Uthayo, assistant police chief and police spokesman, said Ms Pannika's social media accounts will be reviewed to see if they violate the Computer Crimes Act. He insisted the investigation is not politically motivated.
On Sunday, Ms Pannika admitted the picture was "inappropriate" and issued an apology, but claimed the combing of her social media was part of an attempt to discredit her by rival politicians.