Signing employment contracts and annexes by SMS: how to do it right
· 3 min read
A contract that starts on Monday, an employee who is 400 kilometres away and a payroll advisor who needs the document signed today. Signing on paper turns every new hire into a race; certified signing by SMS settles it in the two minutes it takes to read the document.
What labour law says
- An employment contract can be concluded in writing or verbally (art. 8.1 of the Spanish Workers' Statute), and when the law requires written form —temporary contracts of more than four weeks, part-time, internships, training— the written form is valid in electronic form: Law 6/2020 and eIDAS (art. 25.1) prevent a signature from being denied effect for being electronic.
- The remote-work agreement must be in writing (art. 6 of Law 10/2021): another document that can be signed this way, with proof of when and by whom.
How it is proven who signed
The employee receives an SMS with a link to the document, reads it in full on the portal and signs by entering a one-time code sent to their phone: the signature is bound to the phone number the company already has in the employee's file. The evidence file records delivery, opening, reading, code verification and signature, with the cryptographic fingerprint of the PDF — if someone later produces “another version”, it is detected.
It is a simple electronic signature, and we say so up front: it enjoys no legal presumption whatsoever (the one in art. 326.4 of the Civil Procedure Act is reserved for qualified services). If challenged, it is proven with the file and an expert report (art. 326.3 of the Civil Procedure Act) — which is exactly what the file is designed to sustain.
What HR departments use it for
- Seasonal contracts and extensions, in volume and in a hurry.
- Annexes: changes of working hours, non-compete agreements, image rights.
- Documented delivery of internal policies, code of ethics, health and safety information — where what matters is proving it was communicated.
- Receipt of equipment and PPE.
Ordinary communication with staff —shifts, notices— does not need a certificate: that is what ordinary SMS or WhatsApp is for, at messaging cost. The certificate is kept for whatever might one day end up in front of a judge.
Three operational details payroll advisors ask about
The employee's number is the key. The signing code arrives on the phone the company declares when sending the document — the same one as in the employee's file. If that number changes, update it before sending: the strength of the proof lies precisely in that link.
The document does not travel by SMS. The SMS carries a link with an expiry date to a secure portal; the full contract is read there before signing. Neither personal data nor salary terms pass through a channel that shows on the lock screen.
The certificate can be verified by third parties. The evidence PDF carries a public verification code: the payroll advisor, a labour inspection or a court can check its integrity on our verification page without asking us for anything. And the file also records the expiry if the employee never signed — knowing that something was NOT signed, with a date, is information too.