The companies which won contracts valued Bt2 million and above are required to file the financial information of the projects to the Revenue Department.
Virote Kongwong, a member of the NACC's sub-committee on public procurements, said that the companies were notified in writing on July 28 of the decision and urged to explain why they failed to comply with the requirement.
The companies which could not clarify this point would be immediately blacklisted, he said. The blacklisting process would kick off in August.
"The number of such companies remains unclear but there should be over 1,000 as some have won 50-60 contracts each," he said, adding that the Revenue Department is yet to receive the financial information of 71,386 projects.