MASC: how to prove the attempt to negotiate so your claim is not rejected

Since 3 April 2025, when Organic Law 1/2025 of 2 January on the efficiency of the Public Justice Service came into force, almost no civil claim gets into a Spanish court without a prior attempt to negotiate. What still goes wrong, eighteen months on, is the evidence. The negotiation happened by phone and left no trace, the burofax went out without certified text, the letter mixed the invitation with the confidential offer. All of this surfaces when the claim is being drafted, which is the worst possible moment.

This piece is about the workflow: what to send, how to prove it arrived, what goes into the case file and how it reaches the claim.

What the law requires, in four provisions

The requirement. Article 5.1 of LO 1/2025 makes prior recourse to an “appropriate dispute resolution method” (medio adecuado de solución de controversias, MASC) a condition for admitting a civil claim, as a general rule. Mediation, conciliation, an independent expert’s neutral opinion, a confidential binding offer or any other legally recognised negotiation all qualify — expressly including direct negotiation between the parties, or between their lawyers on their instructions and with their agreement, and collaborative law. The subject of the negotiation must match the subject of the litigation, even if the specific claims vary.

The exceptions. Article 5.2 applies the requirement to all declaratory proceedings in Book II of the Civil Procedure Act (LEC) and the special proceedings in Book IV, with a closed list of exceptions (fundamental rights, parentage, support measures for persons with disabilities, summary protection of possession, bill-of-exchange proceedings, among others). Article 5.3 adds enforcement claims, pre-action interim measures, preliminary inquiries and, with caveats, voluntary jurisdiction. The monitorio order-for-payment procedure is not on the list, and the courts have not been consistent on how it fits; when in doubt, send the invitation.

The claim. The reform added a fourth item to article 264 LEC: the claim must be accompanied by the document proving the negotiation attempt. Article 399.3 requires the claim to describe the prior negotiation process, and article 403.2 makes failure to meet these requirements a ground for rejecting the claim at admission.

The proof. Article 10 of LO 1/2025 is the one to keep printed. Without a neutral third party, the attempt is proved by a document signed by both parties (identity, date, subject, meetings and a declaration of good faith) or, failing that, by “any document proving that the other party received the request or invitation to negotiate or, where applicable, the proposal, on what date, and that it was able to access its full content”. Where a neutral third party was involved, that person issues the certificate.

Three facts, then: receipt, date and full content. The whole workflow is about being able to prove all three.

The deadlines that drive the calendar

• Thirty calendar days. Under article 10.4.a), the process is deemed ended without agreement if thirty calendar days pass from receipt of the request with no first meeting and no written reply. Once negotiation is under way, article 10.4 adds further cases: thirty days from a specific proposal without a reply, three months from the first meeting without agreement, or written notice ending the negotiations.
• One year. Article 7.3 requires the claim to be filed within one year of receipt of the request or of the negotiation ending without agreement; otherwise the requirement is not met.
• Limitation periods. Article 7.1 interrupts limitation (prescripción) and suspends time-bars (caducidad) from the date the attempt to communicate the request is recorded, provided the request adequately defines the subject. Time restarts or resumes, respectively, if there is no first meeting and no written reply within thirty calendar days.

If you cannot prove the date of the attempt, you cannot prove the interruption either. How to keep those periods under control in a firm is covered in the piece on limitation and time-bars.

What to send: two documents, not one

The law itself complicates the evidence. Article 9 makes the negotiation process and its documentation confidential, except for whether the parties took part in the attempt and the subject of the dispute. If the letter you plan to file with the claim contains your financial offer, you are filing negotiation documentation.

The practical answer is to split it:

1. The invitation, written to end up as an exhibit to the claim: identity of the parties, the specific subject of the dispute (contract, invoices, amounts), the method proposed, contact details, a deadline to respond and an express reference to LO 1/2025. No figures offered.
2. The proposal, if any, as a separate document marked confidential.

This is not settled ground, since article 10.2 refers to the full content of the invitation “or, where applicable, the proposal”. But an invitation that properly defines the subject interrupts limitation under article 7.1 and can be filed without a confidentiality argument.

How to send it: the channel determines the proof

A burofax with acknowledgement of receipt and certified text remains the standard, because it proves all three things at once: who sent it, what it said and when it was delivered or delivery was attempted. Certified email services from a trust provider do the same job if they certify content, delivery date and, ideally, opening.

The non-judicial plenary of the Provincial Court of Salamanca, on 22 April 2026, accepted as valid channels post with acknowledgement of receipt, burofax, SMS burofax, buromail or email, WhatsApp (by majority) and any other means that records sending and receipt, and required the channel to establish the sender’s identity, receipt, date and content. That is one court’s criterion, not a general rule. What works nowhere: a phone call with no signed note afterwards, or an email to an address the other side has never used with you.

The uncollected burofax. The Provincial Court of Navarre, in orders 413/2025 of 5 December and 423/2025 of 12 December, held the requirement met where the burofax had been sent to the address designated for notices and was never received, overturning the first-instance rejections. The Salamanca criteria point the same way: a delivery notice left and not collected can be treated as valid where non-delivery is due solely to the addressee’s will or inaction. The operational lesson is to send to the contractual address, or the one used in previous dealings, and keep the delivery-notice and return slips.

What can be cured and what cannot

The published criteria agree on one distinction. The Las Palmas first-instance judges’ agreement of April 2025 and the Salamanca plenary of 2026 both take the view that an omitted MASC cannot be cured; Salamanca says it outright: once the claim is filed, the negotiation can no longer take place. By contrast, failing to attach or mention the supporting document is widely treated as curable. On omitting the description required by article 399.3, the provincial courts diverge.

In short: if you negotiated and forgot to attach it, you have room; if you did not negotiate, you do not. And how much room depends on the court, so do not design your workflow around it.

A worked example with dates

A corporate client is owed €18,400 in unpaid invoices by another company. On Tuesday 16 June 2026 the firm sends the invitation by burofax with acknowledgement of receipt and certified text to the registered address stated in the contract. It is delivered on Thursday 18 June.

• 18 June: delivery. Limitation is interrupted from the date of the attempt to communicate, which the burofax itself certifies.
• 18 July 2026 (Saturday): thirty calendar days from receipt without a reply. The process is deemed ended without agreement and the limitation period starts running again.
• 18 June 2027 (Friday): end of the one-year window under article 7.3 to file the claim with the requirement met.

Had the debtor replied on 3 July asking for time to pay, the file moves into a different phase: negotiation is open and the clock switches to the article 10.4 cases (thirty days from each specific proposal, three months from the first meeting). Every written reply is filed with its date.

What to keep in the case file

Evidence gets lost through dispersion. The minimum that should sit in the matter before the claim is drafted:

• The invitation as a PDF, with its text certification.
• Proof of delivery or, where applicable, the delivery notice and return.
• The confidential proposal, separate and marked as such.
• Every reply from the other side, with channel and date.
• A note of the calculated dates — limitation interrupted, day 30, end of the article 7.3 year — each with a calendar alert.
• A draft of the article 399.3 paragraph describing the process, written while the facts are fresh, not a year later.

Our view: write the invitation as exhibit 1 to the claim, because that is what it will be. If you draft it with the admitting judge in mind, the rest follows. And in deals with a fixed date, such as a property transaction that goes wrong, send it early: the thirty days do not wait.

How Mandato handles it

In Mandato, each matter has its case file, and the MASC phase is run inside it: the invitation, the burofax certification, replies received by email or WhatsApp in the firm’s shared inbox, and the control dates sit in one place, with their deadlines in the calendar. The AI inside the case file can propose a draft of the article 399.3 description from the filed documents, which the lawyer reviews and corrects. More in the case management guide and on the page for civil litigation firms. The certified sending itself is done by your postal operator or trust provider; what Mandato prevents is the proof ending up lost in someone’s personal inbox.