Doing work for any employer in Thailand, paid or unpaid is illegal on a tourist visa.
Lets quote the act you link to:
"To be able to legally work in Thailand the foreigner must have a valid non-immigrant visa and a work permit issued in his name allowing him to perform a specific job at a specific location for a specific company in Thailand."
Now a naive look at this paragraph might leave you with the impression you can be self employed or work for a foreign company.
The fact is that it's impossible to work for a foreign company in Thailand. They need to open local offices and incorporate here. It's also impossible to become self employed without opening a Thai company if you are a foreigner.
So the leading paragraph is correct. You need a work permit to work for a Thai company because all work must be conducted through a Thai company.
Actually, there was an episode of the "Travel Like A Boss" podcast, which is about digital nomadism, where the host and others were taken downtown by the Thai police after a raid on a co-working space. After the police found out that they were paying to do work at the co-working space on unrelated businesses and weren't being paid by the co-working space they let them go without charges [1].
Doing work for any employer in Thailand, paid or unpaid is illegal on a tourist visa.
Lets quote the act you link to:
"To be able to legally work in Thailand the foreigner must have a valid non-immigrant visa and a work permit issued in his name allowing him to perform a specific job at a specific location for a specific company in Thailand."
Now a naive look at this paragraph might leave you with the impression you can be self employed or work for a foreign company.
The fact is that it's impossible to work for a foreign company in Thailand. They need to open local offices and incorporate here. It's also impossible to become self employed without opening a Thai company if you are a foreigner.
So the leading paragraph is correct. You need a work permit to work for a Thai company because all work must be conducted through a Thai company.