When you quit your job in Thailand and the employer has to cancel your visa, do we necessarily have to give them the original passport so that they can cancel the visa or can it be done on a copy of the employee's passport, without giving the original passport?
Many people get confused about the difference between a visa and an extension of stay. A visa is obtained overseas that gives permission to enter the country; an extension of stay is obtained within the country and allows you to stay until a specified date.
Usually when getting a work permit, an extension of stay based on employment is issued with a 'must leave by' date that is the same as the expiry date as the work permit. If you already have an extension of stay for another reason (e.g. based on marriage) then either the previous extension is cancelled, or no new extension is issued. They generally prefer to cancel any previous extension and issue a new one, simply because it then means that there is only one date when you need to update the work permit and extension of stay.
When you leave a job in Thailand and you are staying in the country on an extension of stay based on employment, your employer is responsible for taking you to the immigration office and cancelling your extension of stay. You must leave Thailand on the same day unless you apply for a seven-day extension that will automatically be given, at the standard cost of 1,900 THB. Your work permit will be cancelled at the same time.
If you are on an extension of stay for any other reason (e.g. marriage), or if you do not have an extension at all and just have a visa, then they can not cancel your stay.
In order to cancel an extension of stay, they require your original passport, so they can enter the new stamps to say that your extension is no longer valid, and also to give you a new stamp containing the date by which you must leave Thailand.
1) Don't confuse a visa (obtained outside of Thailand at embassy or consulate) with an extension of stay (obtained within thailand at a local immigration office).
2) You are on an extension of stay for a specific reason: In this case employment. The day that you quit or the day that you are terminated, your extension is technically invalid on that day. But in practice, it may take a few days for your employer to notify immigration, ministry of labor, etc. Some employers may never actually contact immigration. That doesn't mean it is valid. It's just that it works in your favor as the computer still shows a valid extension. But I don't recommend relying on this as you risk being in an overstay condition.
3) You can do what a friend recently did: do an out-in border run immediately. If questioned, explain to the border official that you quit your job or you are getting a new job, so the current extension is not valid anymore. Because they might think you are simply wanting to leave, but forgot to get a re-entry permit as the computer still shows a valid extension. You can also go to local immigration to ensure the existing extension is cancelled and get 7 day extension for 1900 baht. But I would try a border run first. Usually cheaper and gives you more options.
4) Another tip: if you are married to a Thai national, do the extension based on marriage. This way if you have a fallout with your employer, your extension is unaffected. OR get a multiple entry non-"O" or "B" visa . You would have to do border runs every 90 days vs 90 day reports at local immigration. But your visa is still valid in case you part ways with employer or get a divorce.
Although it is getting more difficult now to get multiple non-immigrant visa than in the past, but for legitimate marriage, work, or retirement, you should still be able to get it. Only time will tell.