A Palang Pracharath Party (PPRP) member has urged police to take legal action against Future Forward Party leader Thanathorn Juangroongruangkit for alleged sedition related to a political gathering on the Skywalk at Pathumwan intersection on Saturday.
Meanwhile, a former Supreme Court judge noted that the rally could also lead to the dissolution of the FFP, citing prohibitions under the law on political parties.
Sonthiya Sawasdee on M filed a complaint against Mr Thanathorn and FFP secretary-general Piyabutr Saengkanokkul with Pathumwan police.
Also named in the complaint were FFP spokeswoman Pannika Wanich and Pitha Limcharoenrat, a party MP.
He accused them of breaking the public assembly law by not seeking prior permission for the rally as well as holding it near Sraprathum Palace. Under the law, rallies must be at least 150 metres away from royal residences.
Mr Sonthiya also accused them of violating Section 116 of the Criminal Code, which bans sedition and stipulates a jail term of up to seven years for a violation. He also alleged that they violated Section 6 of the constitution, which stipulates that the King commands respect and shall not be violated.
Metropolitan Police Bureau commissioner Pol Lt Gen Pakkapong Pongpetra said that so far, 11 people who said they were inconvenienced by the rally have been questioned by police, he said.
Those involved in organising the rally may face charges of holding a public gathering without permission from authorities, blocking the use of public services and failing to control rally participants, Pol Lt Gen Pakkapong said.
Pol Col Kissana Phathanacharoen, a deputy spokesman for the Royal Thai Police, said that the organisers of Saturday's event did not seek permission, adding that the public assembly law allows people to hold rallies, though they must obtain permission first.
The rally was called by Mr Thanathorn after the Election Commission (EC) decided to ask the Constitutional Court to consider disbanding his party for allegedly violating the organic law on political parties for accepting a 191-million-baht loan from him to finance its election campaign.
If the court agrees with the EC, the party's 15 executives -- including Mr Thanathorn, Mr Piyabutr and Ms Pannika -- will be banned from politics.
If the party is disbanded, its MPs still have 60 days to switch to new parties and retain their MP status according to the constitution.
The Constitutional Court disqualified Mr Thanathorn as an MP last month after ruling he possessed shares in a media company when he registered his candidacy for the March 24 general election.
Former Supreme Court judge Chuchart Srisaeng on M wrote on his Facebook page that the rally could also lead to the dissolution of the FFP.
He cited Section 45 of the law on political parties, which prohibits parties and party executives from encouraging or supporting anyone to cause a public disturbance or threaten peace and order.
He also cited Section 92 (3) of the same law which allows the EC to forward a dissolution case against a party to the Constitutional Court if there is evidence a party commits actions prohibited by the law, such as in Section 45.
Under the law, party executives who violate Section 45 are also liable to a jail term of up to 10 years and/or a fine of up to 200,000 baht, and to have their election candidacy registration rights suspended for a period of time as ordered by the court.
Ms Pannika said earlier the rally was not unlawful as it was an expression of the people's civil rights under the coup-sponsored charter.
Meanwhile, the FFP on M voted to expel four MPs who have continually voted against the party in parliament.
A general meeting voted 250-5 to axe MP for Chiang Mai Srinuan Boonlue, MP for Chon Buri Kawinnart Takee and two MPs representing Chanthaburi province, Charuek Sri-on and Pol Lt Col Thanapat Kittiwongsa.
Deputy party spokesman Natcha Boonchaiinsawat said the decision will be forwarded to the party executive for approval. The renegade members will then have 30 days to join new parties, or lose their seats.