How to deal with a supplier about non-written specification: what to implement now when you can't wait for an official change

When you need to deal with a supplier about a non-written specification and can't wait for a formal change, document the requirement immediately in a temporary deviation or interim control, get written supplier acknowledgment, and start the official change process in parallel. Don't let the absence of a signed document become the absence of any action.

You found a problem. The supplier shipped parts that don't meet what everyone on your team knows is a requirement - except nobody ever wrote it down. No drawing callout, no PPAP note, no work instruction. Just tribal knowledge, a few old emails, and the memory of a verbal agreement from two product launches ago. Knowing how to deal with a supplier about a non-written specification - right now, before the paperwork catches up - is the skill that keeps your line running.

You have a production line at risk, a supplier pushing back, and your change management process moving at its usual glacial pace. How do you act before an official document ever gets released?

This is the situation nobody prepares you for in a quality manual. Let's work through it.

Why unwritten specifications are so common - and so dangerous

Reality check: unwritten specifications exist at almost every manufacturer. They show up when a customer gave a verbal instruction during a launch review. When an engineer adjusted a parameter on the floor and never updated the drawing. When "everyone knows" a certain surface finish is required but it never made it into the PPAP package.

They're dangerous for one simple reason: they're invisible to your supplier. If it's not in a document they signed, they have no legal or contractual obligation to follow it. And when a quality dispute hits, they will say exactly that.

The skilled-labor shortage has made this worse. Experienced engineers retire and take their unwritten knowledge with them. New suppliers come on board with no context. What used to be a shared understanding becomes a gap - one that only surfaces when something goes wrong.

If your organization is losing institutional knowledge faster than it's capturing it, that's a systemic problem worth addressing separately. Knowledge management in manufacturing: can it prepare you for any trouble? covers exactly that angle.

What's your actual exposure right now?

Before you do anything else, assess the risk. Not every unwritten specification gap carries the same urgency.

Ask yourself three questions:

1. Safety or regulatory? If the missing specification touches a safety-critical function or a regulatory requirement (emissions, crash performance, electrical insulation), stop incoming material and escalate immediately. There is no workaround here.

2. Customer-facing? Will a nonconforming part reach your customer? If yes, containment comes before everything. Check stock, check what's already shipped, and get ahead of a potential customer claim. The moment you suspect parts may have escaped, the clock starts on your response. See Reaction to a customer claim - what to do and what to avoid for a clear sequence.

3. Functional or aesthetic only? If the gap is lower risk, you have slightly more room to maneuver. A 100% incoming inspection buys you time while you fix the documentation.

Once you know what you're dealing with, you can prioritize. Don't treat a cosmetic ambiguity the same way you treat a structural specification gap. Separate them and act proportionally.

How do you implement a control right now without an official change?

This is the core practical problem. You can't wait six weeks for your engineering change process to grind through approvals. You need something today.

Here's a step-by-step approach:

Step 1: Write a Temporary Requirement Document. Call it a Temporary Deviation, an Interim Engineering Standard, or a Supplier Letter of Requirement - whatever your system supports. The name matters less than what it contains: the specific requirement, the measurable acceptance criterion, the effective date, and the signatures of your quality manager and the responsible engineer. Two pages is enough. This is not a permanent document; it's a bridge.

Step 2: Get written acknowledgment from the supplier. Send the document to your supplier contact and ask for a signed return confirmation. Email acknowledgment is acceptable if a formal sign-off isn't possible within your timeframe. You need something on record showing they received and understood the requirement. A verbal conversation is not sufficient.

Step 3: Define a measurement or inspection method. An unwritten specification often means there's also no agreed measurement method. Specify exactly how conformance will be verified - a gauge, a visual standard, a functional test. Attach reference photos or an approved boundary sample if you have one. Without this, you'll have the same argument next shipment.

Step 4: Update your incoming inspection until the formal document is live. Adjust your control plan to add a receiving inspection step that references your temporary document. Log results. This data becomes evidence if the supplier disputes the requirement later.

Step 5: Start the formal change process immediately - in parallel, not after. The temporary document is not the solution; it's containment. The solution is a properly controlled specification in your engineering system. Assign an owner, set a target date, and track it. If your organization has a habit of letting temporary fixes become permanent, this is where that pattern breaks.

How do you communicate this to the supplier without triggering a dispute?

Tone matters here. If your first message to the supplier reads like an accusation, you'll spend the next two weeks in commercial arguments instead of fixing the problem.

Frame the communication as a clarification. Something like: "We've identified that our documentation does not fully capture a requirement that has been part of our product standard. We are issuing interim documentation to clarify this expectation effective immediately. Please confirm receipt and advise if you have any questions about measurement or conformance."

Reference the closest existing document you have - an approved sample, a PPAP record, a customer-specific requirement, an old email thread. Don't claim the requirement was always documented if it wasn't. Suppliers can check. But you can absolutely point to intent, prior practice, or industry standard as supporting evidence.

Set a clear effective date. Don't make it retroactive if you can avoid it - that's where commercial disputes start. Focus on what happens from the next delivery forward.

What if the supplier refuses to accept the requirement?

This happens. Especially if the requirement creates additional cost or processing for them.

If they push back:

• Escalate internally to your supplier quality engineer and purchasing team. This is no longer a technical conversation; it's a commercial one.

• Check whether the requirement originates from your customer. If it does, pull their specification or customer-specific requirements and reference them directly. That changes the conversation - now it's your customer's requirement, not just yours.

• Trigger a formal corrective action request to the supplier. This creates an official record and signals that the issue is tracked.

• If the gap is genuine and the supplier's position is defensible, acknowledge that a formal engineering change is the right resolution and give them a timeline.

The question of whether you have a quality engineer with the authority and expertise to manage this kind of supplier escalation is worth asking. Do companies need a quality engineer? A reality check for manufacturers addresses that directly if your team is still debating the role.

What do you absolutely need to document before the official change is released?

Before a formal specification exists, your protection comes entirely from your paper trail. Make sure you have:

• The temporary requirement document, signed and dated

• Supplier acknowledgment in writing (email counts)

• Updated incoming inspection records referencing the interim requirement

• Any evidence of prior practice: approved samples, historical inspection data, customer correspondence

• A corrective action or engineering change request with an assigned owner and target date

That file is what protects you if a customer claim arrives, if a supplier disputes liability, or if an auditor asks why a production control existed without a formal document to back it up.

The deeper problem this situation points to

A specification gap like this rarely appears in isolation. It's usually a symptom: of a product launch that moved too fast, of a change that was implemented on the floor but never captured in the system, of an organization where technical knowledge lives in people's heads rather than in controlled documents.

Fixing this one gap is necessary. But if your team handles it quietly and moves on, the same gap will reappear somewhere else - with a different supplier, a different part, a different engineer who's no longer available to explain what "everyone knows."

The corrective action for an unwritten specification isn't just the document. It's the process that should have created the document in the first place. Root cause analysis applied to your own documentation process is uncomfortable but necessary.

FAQ: dealing with non-written specifications and supplier disputes

Can you hold a supplier accountable for a specification that was never written down?
Yes, but it's harder without documentation. Your best tools are industry standards (like IATF 16949 or customer-specific requirements), prior approved samples, and any email or meeting record where the requirement was discussed. Document everything retroactively and get supplier sign-off on a temporary requirement sheet as your first move.

What is the fastest way to implement a control without waiting for an official specification change?
Issue a Temporary Deviation or Interim Engineering Standard signed by your quality manager and the relevant engineering owner. It documents the requirement now, gives the supplier something to reference, and creates the paper trail your formal change process will need later.

How do you communicate an unwritten specification to a supplier without causing a commercial dispute?
Frame it as a clarification, not a retroactive demand. Reference the closest existing document (drawing note, PPAP, or approved sample), state what the current expectation is, and set a clear effective date. Focus on the product requirement, not blame.

What happens if the supplier refuses to accept a non-documented requirement?
Escalate immediately to your supplier quality engineer and commercial team. In parallel, trigger containment on incoming material and check your customer's own specification package for any implicit requirement you can reference. If the gap is real, a formal engineering change is unavoidable - start that process now even if it's slow.

Should we stop production while we sort out the specification gap?
Not automatically. Assess the risk first: does the missing specification create a safety, function, or regulatory issue? If yes, stop and contain. If it's a grey area, implement a 100% incoming inspection as a temporary measure and keep production running while you resolve the root cause.

Unwritten specifications are a reality in manufacturing. They don't go away on their own, and they don't wait for your change process to catch up. What you do in the next 48 hours - the temporary document, the supplier communication, the inspection update - determines whether this becomes a contained problem or a customer claim you're explaining next month.

Act now. Fix the documentation. Then fix the process that let it stay unwritten.