Barbed wire has been installed at the Crown Property Bureau as police warn protesters who planned a rally there on Wednesday the place is off-limits.
Barbed wire was seen on the bureau's walls on Nakhon Ratchasima Road in Bangkok on Monday ahead of the protest that organisers had promised to accelerate campaigns against the government.
The bureau is another target by the demonstrators. They demand reform of the monarchy, the resignation of Prime Minister Prayut Chan-o-cha and a new charter.
The new rally site was announced after Parliament dumped a charter amendment draft proposed by Internet Law Reform Dialogue (iLaw) on behalf of almost 100,000 people. The so-called people's version was the only one of seven that did not restrict changes to be made in all chapters of the constitution. Others prohibit changes to the chapters on the rule of the country and the King.
Pol Lt Gen Pakkapong Pongpetra, commissioner of the Metropolitan Poice Bureau, on Monday warned protesters not to go within a 150m radius from the office. Assembling within the distance from palace grounds is prohibited under the Public Assembly Act.
The rally will be held amid concern that royalists will stage a counter demonstration.
Prime Minister Prayut Chan-o-cha said he would not allow a clash between the two groups and said legal action will be taken on both sides if they turn violent.
Both sides briefly clashed at Kiakkai intersection on Wednesday when MPs and senators were debating the seven charter-amendment bills.