The HR Documents You'll Issue Most Often in Thailand: Warning Letters, Resignation Letters, Employment Certificates

An employment contract gets signed once, at the start of the relationship. But warning letters (หนังสือเตือน), resignation letters (ใบลาออก), and employment certificates (หนังสือรับรองการทำงาน) come around again and again in every company: every time there is a disciplinary issue, every time someone resigns, and every time a former employee asks for proof of employment.

The problem is that HR staff or SME owners without an in-house legal team usually have to produce these documents in a hurry, without knowing what the law actually requires. This article explains the correct rules for all 3 documents, plus how to send them for signature or acknowledgment properly.

TL;DR: An employee warning letter stays effective for roughly 1 year from the date of the misconduct. There is no fixed "three warnings and you can dismiss" rule, despite the common belief. On resignation, the law calls for at least one pay cycle of advance notice, but a resignation takes effect even without proper notice; the employer may sue for damages if it can prove actual loss. And employers are legally required to issue an employment certificate when an employee requests one. This article covers all 3 documents plus how to get them signed properly online.

What you'll learn in this article

• Why these 3 documents differ from the employment contract: they recur, they aren't one-offs
• How long a warning letter stays valid, and where the "three warnings" myth goes wrong
• How much notice an employee really has to give before resigning, and what happens without it
• Whether an employer can refuse to issue an employment certificate
• How to move from paper documents to signed documents with clear evidence

The 3 HR documents that keep coming back in every company

An employment contract is signed once per working relationship. Warning letters, resignation letters, and employment certificates recur every time something happens: every disciplinary issue, every resignation, and every former employee who comes back asking for written confirmation.

That is why these 3 documents deserve a clear process set up in advance, rather than digging out an old Word file to edit at the last minute. If you already have a complete employment contract, these 3 documents are the steps that follow across an employee's entire lifecycle, from active employment through to after they leave the company.

Employee warning letters: how to write one that actually has legal effect

A warning letter stays effective for roughly 1 year from the date of the misconduct, and there is no fixed "three warnings and you can dismiss" rule, despite the common belief.

What determines whether an employer can dismiss without severance is a repeat of the same offence while the warning letter is still in effect, not a fixed count of warnings. If the employee repeats the same misconduct after the warning letter has expired, it counts as a fresh offence, not a repeat under the old warning.

A warning letter with real legal effect should contain:

• The issue date, stated clearly
• A factual account of the actual misconduct, written as facts rather than vague labels like "bad attitude" that are hard to prove later
• A reference to the work rules, where a relevant regulation exists
• The employee's acknowledgment signature, or evidence of delivery if the employee refuses to sign

The most common mistake is describing the misconduct in vague terms without clear facts. When the warning letter is later needed as evidence, it becomes impossible to prove what the employee actually did wrong.

Resignation letters: how much notice does an employee really have to give?

The law calls for at least one pay cycle of advance notice, but a resignation is effective and complete even without proper notice. This is the point to get exactly right, because employers and employees tend to get it wrong in opposite directions.

Both sides of this need emphasis: it is not correct to say "you cannot resign without advance notice" (the resignation still takes effect), and it is equally incorrect to say "skipping the notice has no consequences at all" (the employer may sue for damages if it can genuinely prove a loss occurred).

What a good resignation letter should contain:

• The intended last working day, stated clearly
• The date the letter was written
• The employee's signature

In practice, an employer cannot force an employee to keep working until the notice period runs out. The resignation takes effect as the employee stated. What the employer can do is decide whether to pursue damages, if there is genuinely provable loss caused by the employee's failure to give proper notice.

Employment certificates: can the employer refuse?

No. An employer has a legal duty to issue an employment certificate when the employee requests one.

The distinction to keep clear is between what is mandatory and what is discretionary:

• Mandatory: the job title and the period of employment
• Discretionary: stating the salary, and any performance assessment

The point that needs particular care: writing negative statements about the employee can expose the employer to defamation liability. The safest approach is to keep the employment certificate purely factual, such as the position and the dates of employment, without adding opinions or personal evaluations.

From paper documents to signed documents with clear evidence

Moving from paper to signed and delivered documents with clear evidence takes only a few steps: upload the document, add the employee's name, send a signing link, and get a signing audit trail with precise timestamps.

For warning letters in particular, the audit trail helps evidence that the employee actually received the notice, which makes a later claim of "I never received this letter" much harder to sustain. Keep the framing accurate, though: this strengthens the evidentiary weight of the document; it is not a guarantee of any particular legal outcome. Documents signed with an ordinary electronic signature are already binding under the Electronic Transactions Act B.E. 2544 (2001); OTP and the audit trail add evidentiary weight on top, as explained in how e-signed documents work as court evidence. If you are choosing a tool for sending HR documents for signature, see the 2026 comparison of Thai e-signature tools.

If your company also needs employees to sign confidentiality undertakings alongside these documents, see the NDA template guide, particularly for staff with access to customer data or sensitive business information.

Frequently asked questions

How long is an employee warning letter valid?

A warning letter stays effective for roughly 1 year from the date of the misconduct. After that period, repeating the same misconduct counts as a fresh offence, not a repeat under the old warning letter.

Is it true you need three warnings before dismissal?

There is no fixed "three warnings" rule, despite the common belief. What matters is a repeat of the same offence while the warning letter is still in effect, not any specific count of warnings.

Is resigning without 30 days' notice against the law?

The resignation is still effective and complete even without the required notice, but the employer may sue for damages if it can genuinely prove a loss caused by the missing notice. Don't treat skipping the notice as consequence-free, and don't treat it as flatly illegal either.

Does an employer have to issue an employment certificate?

Yes, when the employee requests one. It is a legal duty. The mandatory content is the job title and the period of employment; stating the salary or evaluating performance is at the employer's discretion.

Does a warning letter need the employee's signature to be usable?

Having the employee sign for acknowledgment strengthens the evidentiary weight, but an employee's refusal to sign does not make the warning letter unusable, as long as the employer can prove the notice was delivered another way, such as through a channel with proof of receipt.

The bottom line

Warning letters, resignation letters, and employment certificates each follow different rules and call for different drafting, but they share one thing: clear evidence protects both sides, employer and employee alike.

If your company issues these documents often, try the templates in the Jabmue gallery and send them for electronic signature to keep clear proof of receipt. Try Jabmue or see current pricing.

This content is general information, not legal advice for any specific case. For anything involving dismissal or severance in particular, consult a labour law advisor about your situation.