The Centre for Maintaining Peace and Order (CMPO) has threatened to launch tax probes into major companies in a bid to stop them providing support for anti-government protesters.
CMPO director and caretaker Labour Minister Chalerm Yubamrung has warned two firms, one selling liquor and the other ducks and chickens, against backing the protesters.
He did not name the companies or say what kind of support he meant.
If the companies do not stop providing help, he will ask the Excise Department and the Revenue Department to investigate them for tax evasion.
Mr Chalerm said one of the companies has so far avoided paying high liquor taxes.
If they try to help overthrow the government, they will also end up facing an insurrection charge, he added.
The centre earlier announced up to 30 companies are backing the anti-government People's Democratic Reform Committee (PDRC), providing funds, shelters, vehicles and other amenities to protesters.
It has already told the firms and business people allegedly involved in the protest to back off.
Department of Special Investigation chief and CMPO member Tarit Pengdith accused businessman Sathit Segal, who is chairman of the Thai-Indian business association, of defying the emergency decree. He has been one of the speakers at the PDRC rallies.
Mr Tarit said he will provide information about foreign nationals who have joined the protest to immigration police for background checks.
According to Mr Tarit, the CMPO had found about 200 million baht worth of deposits were made to the PDRC's bank account, Khrua Ratchadamnoen, opened to receive financial donations from its supporters, over the past two months.
Mr Tarit said there have been intelligence reports about some residents from the South being brought to Bangkok to help blockade poll venues on Sunday.
He warned individuals as well as the transport firms involved in ferrying the protesters to Bangkok that they will be prosecuted.
The centre yesterday decided to appoint the secretary-general of the Anti-Money Laundering Office to work with the Revenue Department and the Royal Thai Police Office to act against firms that assist PDRC co-leaders.
Mr Chalerm said he would treat financial aid to the protest seriously in order to restore peace to the country.
PDRC spokesman Akanat Promphan said PDRC secretary-general Suthep Thaugsuban yesterday discussed safety measures with protest co-leaders to set the date and time to mobilise supporters in an effort to seize the CMPO headquarters, currently located at the Narcotics Suppression Bureau on Vibhavadi Rangsit Road.
He said the PDRC suspended plans to lead protesters to the headquarters on Wednesday.
Mr Akanat said the PDRC co-leaders have mapped out guidelines for staging their move on Sunday.
Mr Chalerm said he would use the Royal Police Cadet Academy in Nakhon Pathom's Sam Phran district as the CMPO's back-up headquarters, denying he was planning to flee the protesters.