No matter what type of work you plan to do during your stay in Thailand, paid or unpaid, you must obtain a work permit from the Ministry of Labour beforehand. This is usually done by the Thai employer, but sometimes has to be undertaken by the individual planning to work in Thailand. You will need a Non O or Non B visa first to be able to apply for your work permit. The best way to do this is to hire the services of a multi-lingual lawyer who speaks Thai and your own mother-tongue.
The Thai law firm you hire can arrange for translation of all documents, and can also help you for the documents to be notarized, before submitting them to the Ministry of Labour office. They can even come with you, when you collect your work permit in person to help with interpreting.
If you're doing the application without a law firm in Thailand, you can apply for a business visa through a Thai consulate or embassy in your home country, stating that you will be employed in Thailand. The embassy or consulate officer dealing with your application may need to see your work permit application (document WP3) at the same time, before a business visa or Non B visa can be issued to you. In addition to this form, you need to present a medical certificate, proof of your degree or professional qualifications and photographs of yourself. The Thai consulate or embassy officer will submit your documents to the Ministry of Labour, after which it will take around 10 business days for your work permit to arrive. If you are travelling to Thailand to take up a position in a company, the consulate or embassy officer will also be asking for proof that you will be employed by a Thai registered company.
Whether or not you will receive a work permit may also depend on the type of job you are asked to perform in Thailand - there are some restrictions on what type of work foreigners may take up in the country. The rules governing these restrictions change from time to time, but a Thai law firm will be able to advise you on the most current situation. You may also be asked to supply a complete Curriculum Vitae, a criminal background check from your home country, and a tax return from your last working time in Thailand, if you are returning to take up a new teaching post for example.
Renewal of your Work Permit
You will need to renew your work permit well in advance of its expiry date. The same documents apply as for the first one, but this time you will need to submit a tax certificate that states you have paid your Thai taxes for the period covered by your first work permit. In addition, you will need a new medical certificate, which must state your blood type and show that a syphilis check has been carried out. Your employer should furnish you with a copy of the company's registration and VAT registration. If the company is licensed to carry out its daily enterprise, you must also provide a copy of the Thai business licence. In addition, you must provide a copy showing that your social security payments have been made.