Thailand's new premier Abhisit Vejjajiva said on Saturday his opponents would be allowed to rally when he delivers his policy address, as a protest group vowed to gather thousands of supporters.
Backers of ousted premier Thaksin Shinawatra, who are known as "Red Shirts" because of the scarlet clothes they wear, have said they will start gathering in Bangkok on December 28 to demand the dissolution of parliament.
Abhisit, voted in by lawmakers on December 15 after a court dissolved the Thaksin-linked ruling party, said police would be able to handle the protest.
"The Red Shirts have a right to rally under the constitution. We must respect their rights, but I have instructed officials to better handle them and not allow them to violate the law," Abhisit told reporters.
Authorities will be keen to prevent a repeat of the events surrounding a rally outside parliament by anti-Thaksin group the People's Alliance for Democracy (PAD) on October 7, when police and protesters clashed, leaving two people dead and nearly 500 hurt.
The PAD began rallying in May, accusing the People Power Party (PPP) government of running the country on behalf of Thaksin, who was removed in a 2006 coup and lives in exile overseas to avoid corruption charges.
Their campaign culminated with the occupation of Bangkok's two airports late last month, which they ended on December 3 after a court disbanded the PPP and forced then-premier Somchai Wongsawat from office.
The move opened up a power vacuum swiftly filled when Abhisit's Democrat Party won over defecting MPs, but supporters of the last government feel the court decision robbed them of their democratic rights.
Jatuporn Prompan, a leader of the Red Shirt group, said they would mobilise thousands of supporters to protest the legitimacy of the Democrat-led coalition.
"This government has no right to rule, you can see minister positions have been awarded to capitalists, the PAD and the military, who helped the Democrats into power," he told AFP.
"We will move to parliament to demonstrate there, but we will not seal off and block lawmakers from entering," he added.
The Democrats are currently awaiting royal approval for their cabinet line-up, and Abhisit is due to deliver his policy address to parliament in the week beginning December 29.