If you are working with an International Non-profit organization. Following Thai laws and regulation, An ermployer obligates to submit application name "PV 4 /4.1" or PVR 4 / 4.1 along with other documents requirements to "The Committee on Consideration of the Entry of Foreign Private Organization". Once the commitee approve, the Foreign Worker Administration shall send an offical letter to employer. this letter is equal to WP 32 for employee apply Non-immigrant B visa at their location. This process will be taken approximately between 5- 10 months. 

With WP 32 letter and Non-Immigrant B in your hand. once you are entering to Thailand. Schedule to visit Department of Employment at your location for submit WP 25 form. They are going to process your application within 5 working day.

In general, the Department of Employment grant work permit 1 year valid. you may renew it 30 days before end date.

Once contract is ended. Employer is obligated to inform The Department of Employment within 15 days after end date. Overdue submission will be penalty between 20,000 - 200,000 THB / case.