Prime Minister Prayut Chan-o-cha will definitely be targeted in a censure debate being launched against the government, according to Sutin Klungsang, the opposition chief whip.
Mr Sutin said Gen Prayut is in the opposition's crosshairs, although he declined to say what the premier will be grilled about.
The opposition has yet to decide which cabinet ministers it will target during the debate.
The opposition is expected to formally file the censure motion by Dec 5, Mr Sutin said.
Topics that could be raised include graft, incompetence, illegal actions, suitability for public office and tarnishing the country's image in the eyes of the international community, he added.
The opposition chief whip revealed sources were currently supplying information about the government's alleged wrongdoing.
Evidence pointing to poor government performance keeps piling up, he said.
Pheu Thai Party secretary-general Anudith Nakhornthap said on Tuesday that the opposition will back the censure motion with information being gathered mainly from its members sitting on the 35 House standing committees.
More than 70% of those surveyed agree with the opposition's plan to bring a no-confidence motion against the government, according to a survey by the National Institute for Development Administration, or Nida Poll.
The nationwide poll was conducted from Nov 6-7 among 1,271 people aged 18 and above.
Asked whether they agreed with the opposition motion to officially condemn the entire government, about 52% of respondents said yes, while 18% said no. The rest were undecided.