Police expect the crowds to surge to about 5,000 later in the day and about four companies of policemen have been deployed to keep the peace. The rally speakers are to address the crowds in the afternoon.
The red shirt move came a day before a joint House-Senate meeting and in the middle of a public dispute over the court's authority to issue the injunction. The court earlier accepted for review five petitions asking it to rule on the legality of the draft constitutional amendment and issued an injunction to suspend the parliamentary process pending a court ruling.
As of today, neither a vote nor consideration of the amendment for its third reading has been put on tomorrow's agenda.
The red shirts are expected to launch a signature campaign to remove the judges following a controversial decision to launch the judicial inquiry into the charter change. They claim nearly 10,000 names have been collected for the petition to impeach the court judges, while an additional 12,000 names will be sent from upcountry by noon today.
Organisers said the rally might last more than one day and that the red shirts would be careful not to spill out into the Royal Plaza where the Dhamma March protesters, seen as allies of the yellow shirts, have been camping since last week to oppose the reconciliation bill.
A number of red-shirt leaders have hinted that the rally would continue tomorrow, coinciding with the Parliament session.
The protesters want lawmakers to complete the passage of the charter change bill in defiance of the court order to put the vote on hold pending the judicial inquiry into the matter.
Security has been tightened around Parliament to avoid possible confrontations as a rival movement, the yellow-shirted People's Alliance for Democracy (PAD), which opposes any move to amend the charter and any deliberation of national reconciliation bills, is gathering at the Royal Plaza, not far from Parliament.
The authorities have set up two-tiers of concrete barricades and 400 police officers have been deployed to maintain law and order.
The Secretariat of Senate reported that Pheu Thai party-list MP Weng Tojirakarn, also a key Red shirt leader, will hand in the impeachment petition against the Constitution Court judges to Senate Speaker Theeradej Meepian at 2pm, giving it to his deputy Pornthip Lohveera Chanrattanapreeda.