The Metropolitan Police Bureau is preparing multiple charges against 16 leaders of the anti-government demonstration in Bangkok last weekend.
Pol Maj Gen Sukhun Prommayon, a deputy commissioner, said on Tuesday that charges would be brought against 16 key protesters, who were in three groups.
One group gathered the people who organised the demonstration without getting authorisation.
The second group consisted of people who invited others to take part in the rally, through all channels.
The third group comprised people who spoke from the demonstration stage.
Police were transcribing their speeches, parts of which were improper, he said.
Bangkok police were also taking legal action against the demonstrators who installed a pro-democracy plaque in the ground at Sanam Luang on Sunday.
This would include a complaint filed by the Fine Arts Department under the Ancient Monuments, Antiques and National Museums Act, which prohibits any change to a heritage area, Pol Maj Gen Sukhun said.
Sanam Luang is included in the ancient monuments and museums law.
The plaque was dug up and removed on Sunday night. No one has admitted seeing who did it.