Protest leader Suthep Thaugsuban has declared that anti-government protesters will be out in force again and "seize Bangkok" after the New Year holiday ends on Thursday.
"We will not leave an inch of this capital city for the people of the Thaksin (Shinawatra) regime to stay in and take advantage of the people," said Suthep, who heads the self-styled People's Democratic Reform Committee (PDRC).
With the stock market and the baht having already fallen, the prospect is making the business community even more nervous.
In its latest note, Kasikorn Research said that if the political stalemate continues into the second half of next year, Thailand's growth will be only 2.5 per cent, compared with 6.5 per cent last year.
With a large chunk of Bangkok's middle-class residents, who support the protests, out of the capital for a five-day festive break, the rally site was relatively quiet on Sunday.
But underlining the potential for sporadic violence, a giant firecracker was thrown at guards near the United Nations building, injuring three of them. This, a day after a member of a student network allied with the PDRC died in a drive-by shooting nearby.
The PDRC has said its supporters will clean the streets around the sprawling rally site today.
Meanwhile, the ruling Puea Thai party has begun putting up election posters, many of them featuring caretaker Prime Minister Yingluck Shinawatra, and urging people to vote on Feb 2.
However, for the second day running on Sunday, registration centres in eight southern provinces were blocked by PDRC protesters, preventing candidates from signing up for the election.
The mid-term election is a major sticking point, with the government determined to proceed with it and the PDRC determined to derail it. The PDRC says it wants the country run by an unelected people's council to institute reforms before an election is held.
Last Saturday night, it showed a short film in English appealing to "the world" for understanding.