Bangkokbiznews published an article about fines and penalties. It starts with a fine of 2,000 Baht and ends with 7 years in prison.
Penalties for Failure to File Form PND 90/91 and Pay Tax
Failure to submit the form or pay tax beyond the deadline is subject to a fine of not more than 2,000 baht in case of failure to submit the form
An additional 1.5% per month of tax payable
The investigating officer issued a summons and found that the form was not filed or the form was submitted but the tax was too low
The penalty is a fine of not more than 2,000 baht in case of failure to submit the form
1 or 2 times the penalty of the tax payable
An additional 1.5% per month of tax payable
The investigating officer issued a summons and found that the intention was not to file the form to avoid paying taxes
The penalty is imprisonment for not more than 1 year or a fine of not more than 200,000 baht, or both
Penalty fee 2 times the tax payable
An additional 1.5% per month of tax payable
Deliberately making false statements/providing false evidence to avoid paying taxes
The prison sentence ranges from 3 months to 7 years
Fines ranging from 2,000 baht to 200,000 baht
https://www.bangkokbiznews.com/news/news-update/1165969