Thaikorn Polsuwan, a leader of the People's Army against Thaksin Regime, refused to elaborate but said the group has decided to escalate its demonstration.
He said there was a report that the cabinet may resort to issuing an amnesty decree instead of having the controversial amnesty bill debated in Parliament.
The government is legally authorised to issue a decree without having to seek Parliament's endorsement.
Thaikorn said an amnesty decree, if promulgated by the government, will be a significant turning point for Thailand's politics but he doubted if the government would make the decision.
He said some group members would file complaints with the Ombudsman, the National Human Rights Commission, the Constitution Court and Administrative Court today against the government for violating their freedom of expression and for misusing its power in invoking the Internal Security Act (ISA) in three Bangkok districts.
The National Anti-Corruption Commission will also be asked to take action against the national police chief for barring people from joining the rally at Lumpini Park, he said.