Forty caretaker senators on Friday petitioned Thailand's Constitutional Court to dismiss Prime Minister Srettha Thavisin over a cabinet appointment which they say breaches the constitution.
The senators object to the appointment of Pichit Chuenban, a former lawyer, as minister to Srettha's office last month during a cabinet reshuffle.
Pichit was jailed for six months in 2008 for contempt of court after an alleged attempt to bribe court officials with 2 million baht ($55,218) hidden in a paper grocery bag. His law licence was suspended for five years by the Lawyers Council of Thailand after the incident.
The senators said they were seeking a court ruling on whether Pichit has the integrity and ethical standards required by the constitution to hold a ministerial position and whether Srettha had breached the law by making the appointment.
"Pichit is not qualified to be a minister but the prime minister still nominated him for the position," Senator Derekrid Janekrongtham told Reuters.
"The prime minister's action may therefore breach ethical standards as well," he said.
Government critics say Pichit was appointed to the cabinet due to his close relationship with a client, ex-premier Thaksin Shinawatra, who returned to Thailand last year after 15 years in exile. Thaksin still wields considerable political influence over the government.
Government spokesman Chai Wacharonke dismissed the senators' accusation, and said the government had carefully vetted Pichit's qualification.
"Our legal team insists that the appointment is lawful and there is no problem with his qualification," Chai told Reuters.
Last year the same senators closed ranks with military-backed parties to block the anti-establishment Move Forward party from forming a government.
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