The Senate speaker election has emerged as another legal hurdle since the royal decree for the opening of the Senate's extraordinary session did not include such an agenda item.
The decree only allows the Senate to choose a justice of the Administrative Court and a member of the National Anti-Corruption Commission (NACC) based on Section 132 (2) of the Constitution.
Surachai Liangboonlertchai won a 96-51 vote to become the new speaker in the election.
A number of anti-government supporters have tried to delay the next election from July 20 to suit the agenda of anti-government protesters who want reform before the election.
They argue that Niwatthamrong Bunsongphaisan, as acting caretaker prime minister, does not have the prerogative to submit the election royal decree to His Majesty the King for endorsement.
"If Mr Niwatthamrong cannot submit the election decree to His Majesty, he won't be able to submit the Senate speaker appointment to the King as well," said Mr Nikhom.
"Besides, the Senate speaker election could be viewed as having conflict of interest under Section 122 because Mr Surachai is the one who called the meeting. He also acted as its chairman and debated on the speaker election in which he later ran," Mr Nikhom.
"In any case, the new Senate speaker will not have full authority without royal endorsement. Without it, a Senate speaker-elect could not call a meeting to performing its duties such as removing Ms Yingluck [Shinawatra], as well as 36 senators and me, who were charged by the NACC of having conflict of interest."
Mr Nikom, a former elected senator for Chachoengsao, had to cease his duties after the National Anti-Corruption Commission decided he, along with 36 senators, had conflict of interest when they voted for a charter amendment for a fully elected senate.