Various splinter groups of the red- shirt movement have announced they will descend on and protest against the Constitution Court if it rules to dissolve the Pheu Thai Party.
The charter court will rule on the constitutionality of the draft charter amendment which would change the composition of the Senate on Wednesday - a ruling many believe could make or break the ruling party and the Yingluck Shinawatra administration.
The government, Pheu Thai and their red-shirt supporters fear the charter court ruling could lead to a repeat of previous dissolutions of the Thai Rak Thai and People's Power parties - the previous incarnations of Pheu Thai.
Wuthipong Kachatham, leader of the Red Shirt Community Radios Group based in Pathum Thani, said several splinter groups of the United Front for Democracy Against Dictatorship (UDD) will put aside their differences and unite to protect the Pheu Thai-led government.
The groups include the People's Radios for Democracy, the People's Power Alliance, and the Red Shirt Community Radios Group.
"If the Constitution Court delivers an illegitimate ruling and interferes with the legislative branch, which has the legitimacy to amend the constitution, or rules to dissolve the Pheu Thai Party, thousands of members of the groups will march to the court and protest against it," he said.
Pongpisit Kongsena, chairman of the People's Power Alliance, said his group and the Red Shirt Community Radios Group will hold a rally at the Lak Si Monument in Bang Khen district in parallel with the UDD-led rally planned on Monday-Wednesday ahead of the court decision.
UDD spokesman Thanawuth Wichaidit said yesterday it was still uncertain if the UDD will hold its rally at Muang Thong Thani because an international conference of the European Union will be taking place there at the same time.
However, Mr Thanawuth said the rally will go ahead as scheduled.
Pheu Thai list-MP and UDD co-leader Korkaew Pikulthong said various red-shirt splinter groups are acting independently of the UDD, although the UDD will try to prevent them from resorting to any violence.
He said the red-shirt groups do not trust the charter court and want it to rule on the case evenhandedly.
Speaking on Blue Sky Channel satellite television, Democrat Party leader Abhisit Vejjajiva claimed the UDD is threatening violence against anti-government protesters on Ratchadamnoen Avenue.
He accused state authorities of aiding the actions of the red shirts while trying to thwart the moves of the Ratchadamnoen protesters who are holding a peaceful and lawful rally.
More than 200 demonstrators from the Network of Students and People for Reform of Thailand yesterday cast their support behind the Constitution Court delivering fair rulings on the petitions against the government.
"Rulings by the court will have significant impact on the ongoing anti-government movements," said Uthai Yodmanee, an NSPRT coordinator.