Costco Prop 65 Requirements: What Suppliers Should Check Before California Members See Your Product

Oct 25

4 min read

Compliance specialist reviewing a product ingredient list beside a sample package at a desk

Costco Prop 65 requirements are a question many food and consumer brands ask late: if my product is sold in Costco, who is responsible for a California warning, and what do I have to provide? We did not find a Costco-published Prop 65 policy, so this guide does not claim one. Instead it explains how the California rules assign responsibility, and what that means for a supplier selling through a big retailer.

Today is October 25, 2026. This is general information and not legal advice. Prop 65 is a technical area, so work with a qualified attorney or compliance specialist.

A note on sources. The responsibility rules below come from a 2016 summary by the law firm BCLP of the regulations that took effect on August 30, 2018. A second source is a blog post by Mike Thrift dated September 19, 2026, which cites no statutes for several of its claims. We flag which statements are uncited. We could not reach California’s official OEHHA site through our tools, so verify every point there.

Who Is Responsible for the Warning

According to the BCLP summary, the 2018 regulations “seek to put the primary responsibility for providing warnings on product manufacturers or suppliers.” Upstream businesses must:

Specifically identify the product that requires a warning.
Give the retailer the warning materials needed and get written or electronic confirmation of receipt.
Renew notices every six months in the first year, then annually.
Notify a retailer within 90 days if a new chemical or endpoint must be added to a warning.

When a Retailer Can Still Be Responsible

The same summary lists situations where retailers remain liable, including:

Their own private label products.
Knowingly causing a listed chemical to be created in a product.
Covering or altering a warning label.
Selling a product without the warning after receiving a warning notice and materials from the supplier.
Having actual knowledge of exposure where no covered manufacturer or supplier exists in California.

It also says retailers can contractually assign warning duties to suppliers. That is the part that matters most to you. We do not know what Costco’s supplier agreement says about Prop 65, so read yours closely and ask your buyer.

Online Warnings

The BCLP summary says that for internet sales, a warning must appear on the product display page or through a clearly marked hyperlink using the word “WARNING,” and that electronic warnings are allowed if they reach the purchaser before or during purchase. If your Costco item is sold on Costco.com, ask who is responsible for the online warning and how it will be delivered.

Claims We Could Not Verify

The 2026 blog post says Prop 65 applies to businesses with 10 or more employees, lists roughly 900 chemicals, and describes fines of up to $2,500 per day per product. The post cites no statute for the penalty figure and several other points. It also says a new short-form warning language becomes mandatory on January 1, 2028, with no citation. We list these as items to check, not facts. Verify the employee threshold, the chemical list, penalties and any new dates on California’s official Prop 65 site or with counsel.

What We Do Not Know

Whether Costco requires specific Prop 65 documentation from suppliers.
How Costco handles warnings in warehouses and on its website.
Whether your product category is likely to trigger a warning.
Which chemicals in your formula, packaging or ingredients are listed.

Your Costco Prop 65 Requirements Checklist

Read your supplier agreement for Prop 65 language, warning duties and indemnification.
Ask your buyer whether Costco requires Prop 65 documentation, and in what form.
Review your formula and packaging against the current Prop 65 list with a qualified specialist.
Test where needed, using a lab that your specialist trusts.
Decide whether a warning is required for your product, and document why.
If a warning is required, agree who prints it, what it says and how it is delivered.
Plan the online warning for Costco.com if your item is sold there.
Create a notice file: the identification of the product, the materials provided and the confirmation of receipt.
Calendar the renewals if notices apply: six months in the first year, then annually, per BCLP.
Review insurance for coverage questions, as our insurance guide explains.

Common Mistakes

Assuming Costco handles it.
Using another retailer’s warning without checking.
Not tracking changes to the chemical list.
Forgetting packaging and components.
Ignoring the online page.
Relying on an uncited blog for penalties or deadlines.

Why This Is a Brand Strategy Issue

A missed warning can turn a successful item into a legal problem and a buyer problem.

Handling Prop 65 on your timeline is less expensive than responding to a notice of violation.

It also shows a buyer that your compliance work is organized.

Work With Fractional Brand Managers

FBM helps emerging brands organize their Costco readiness file, including the compliance questions buyers and auditors raise. We are not lawyers and do not give legal advice, but we will help you ask the right questions and gather the right documents with your counsel.

Call 732-433-7873 | info@fractionalbrandmanagers.com | www.fractionalbrandmanagers.com

This article is general information, not legal advice. Prop 65 rules change; one source is a 2016 law firm summary and another is a 2026 blog with uncited claims. Verify with California’s OEHHA and a qualified attorney. We are not affiliated with Costco Wholesale.

Summary

Costco Prop 65 policy: not found
Primary warning duty (per BCLP): manufacturers and suppliers
Retailers: can assign duties by contract; remain liable in listed situations
Online sales: warning on the product display page or by marked link
Uncited claims to verify: 10-employee threshold, penalty amounts, 2028 short-form date