Srinual Boonlue is facing a disciplinary probe by the Future Forward Party (FFP), becoming its second MP to be quizzed in two days for defying the party line in a vote in parliament.
The party has appointed a team to probe the Chiang Mai MP for abstaining in a vote on the government-sponsored executive decree to transfer army units to the royal command. The party had decided to vote against the decree.
FFP deputy leader Chamnan Chanrueng said on Tuesday Ms Srinual will be called to explain herself to the investigation team after the by-election in Nakhon Pathom's Constituency 5 on Wednesday. The FFP is standing in the poll to defend its seat.
Mr Chamnan said the abstention might erode people's trust and confidence in the party or confuse supporters about the party's stance.
The party will decide whether Ms Srinual had broken its disciplinary and ethical codes of conduct and, if so, what punishment she will face.
On Monday, Kawinnart Takee, an FFP MP for Chon Buri, was barred from party activities pending the result of an internal probe.
Mr Kawinnart's conduct came under investigation after he twice voted against the party in parliament. He voted in favour of the army unit transfer decree and the 3.2-trillion-baht spending plan for the 2020 fiscal year.