The following is supplied as a general guide. DO NOT take anything as absolute, as with many things in Thailand, there is rarely consistency, and you should always consult with a qualified professional for advice or speak directly to the Ministry of Labor for Thailand for the current situation and regulations.
For all those who are keen on working in Thailand, be aware that there is a list of jobs where you, as a westerner will not be able to get a work permit. The List is taken from The Thai Labor Department Website -http://www.mol.go.th/-
1.- Labour work, except labour work in fishing boats under the next category below. The said work which is forbidden to aliens shall not apply to aliens who have entered into Thailand under an agreement on hire of labour concluded between the Government of Thailand and other nations, and also aliens whose status has been prescribed as legal immigrant and who possess a residence certificate under the law governing immigration.
2.- Agriculture, animal husbandry, forestry or fishery, except work requiring specialised knowledge, farm supervision, or labour work in fishing boats, particularly marine fishery.
3.- Bricklaying, carpentry, or other construction work.
4.- Wood carving.
5.- Driving motor vehicles or vehicles which do not use machinery or mechanical devices, except piloting aircraft internationally.
6.- Front shop sales and auction sale work.
7.-Supervising, auditing, or giving service in accountancy, except occasional internal auditing.
8.-Cutting or polishing precious or semi-precious stones.
9.- Haircutting, hairdressing, or beautification.
10.- Cloth weaving by hand.
11.- Mat weaving or making utensils from reed, rattan, jute, hay, or bamboo.
12.- Making rice paper by hand.
13.- Lacquer work.
14.- Making Thai musical instruments.
15.- Niello work.
16.- Goldsmith, silversmith, or gold/copper alloy smith work.
Stone work.
17.- Making Thai dolls.
18.- Making mattresses or quilts.
19.- Making alms bowls.
20.- Making silk products by hand.
21.- Making Buddha images.
22.- Knife making.
23.- Making paper or cloth umbrellas.
24.- Making shoes.
25.- Making hats.
26.- Brokerage or agency except in international trading.
27.- Professional civil engineering concerning design and calculation, systemization, analysis, planning, testing, construction supervision, or consulting services, excluding work requiring specialized techniques.
28.- Professional architectural work concerning design, drawing/making, cost estimation, or consulting services.
29.- Dressmaking.
30.- Pottery.
31.- Cigarette rolling by hand.
32.- Tour guiding or conducting.
33.- Hawking of goods & Thai typesetting by hand.
34.- Unwinding and twisting silk by hand.
35.- Clerical or secretarial work.
36.- Providing legal services or engaging in legal work, except arbitration work; and work relating to defence of cases at arbitration level, provided the law governing the dispute under consideration by the arbitrators is not Thai law, or it is a case where there is no need to apply for the enforcement of such arbitration award in Thailand.