California SB 253 and U.S. Automotive Suppliers: What the Reporting Requirement Means for You

If you supply the automotive industry and someone has mentioned SB 253, the first thing worth knowing is this: the law almost certainly does not apply to your company.

The second thing worth knowing is that it will still generate work for you.

California's Climate Corporate Data Accountability Act applies to companies with more than $1 billion in annual revenue that do business in California. That threshold excludes the overwhelming majority of automotive suppliers — every Tier 3 machine shop, nearly every Tier 2 component manufacturer, and a good number of Tier 1s.

But SB 253 requires covered companies to report Scope 3 emissions. And an automaker's Scope 3 is, in large part, its supply chain.

The obligation lands on your customer. The data has to come from you.

This guide covers what SB 253 actually requires, why the automotive supply base is more exposed than most industries, what your customers are likely to ask for, and what to have ready.

What SB 253 Requires

SB 253 requires covered entities to publicly disclose their greenhouse gas emissions, verified and reported to the California Air Resources Board.

• Who is covered: business entities formed under U.S. law with total annual revenues above $1 billion that do business in California.
• What "doing business in California" means: being organized in California, or having California sales above an inflation-adjusted threshold (roughly $757,000 for 2025), or California sales representing 25% of total sales.
• What gets reported: Scope 1 and Scope 2 first, with Scope 3 following in a later phase.
• Penalties: up to $500,000 per entity per year.

Notice how low the California nexus test is. A company with $757,000 of California sales qualifies as doing business there. For a manufacturer of any scale, that is trivially met.

So the real filter is the $1 billion revenue threshold — not geography. Which is exactly why the law captures automakers and large Tier 1s almost completely, while leaving the companies that supply them outside its scope.

Where Things Currently Stand

SB 253 is still being implemented, and the details have moved more than once. As of September 2026:

• First Scope 1 and Scope 2 reports are due November 10, 2026, covering fiscal years ending in 2025. CARB deferred this from the original August 10, 2026 date while it made revisions to the implementing regulations.
• Scope 3 reporting begins in 2027, on fiscal year 2026 data.
• Assurance is not required for the 2026 reports. Limited assurance requirements are expected to begin with the 2027 cycle.
• A safe harbor applies to good-faith Scope 3 disclosures through 2030, acknowledging that supply chain data will be imperfect early on.
• Litigation is unresolved. A First Amendment challenge to both SB 253 and SB 261 is before the Ninth Circuit, argued in January 2026, with a decision pending. Importantly, the court enjoined enforcement of SB 261 in November 2025 but declined to do the same for SB 253.

Two practical implications follow. First, SB 253 has not been paused — unlike SB 261, it is proceeding. Second, because rulemaking is ongoing and an appellate decision could land at any time, treat any specific date in this article as current-as-of-writing rather than settled. Your customers' compliance teams are tracking this closely; it is reasonable to ask them what they are planning against.

Why This Reaches Automotive Suppliers Specifically

Three features of this industry make the cascade sharper here than almost anywhere else.

Essentially every automaker is a covered entity

California is the largest automotive market in the United States. Every major OEM sells there, far above the nexus threshold, and comfortably clears $1 billion in revenue. There is no meaningful population of automakers that escapes SB 253 on scope. The same is true of most large Tier 1 systems suppliers.

Purchased goods dominate an automaker's footprint

A company that assembles vehicles from thousands of bought-in components holds only a small share of its total emissions inside its own plants. Scope 3 is the majority, and Category 1 — purchased goods and services — is the largest piece of it.

An OEM cannot produce a credible Scope 3 figure from its own records. It has to ask.

Transportation is a candidate for the first Scope 3 phase

CARB has been consulting on how to phase in Scope 3 reporting, and one option under consideration is a sectoral approach that begins with the sectors contributing most to statewide emissions — with transportation named among them.

That is not settled, and it may not be the approach adopted. But it means automotive is a plausible candidate to be early rather than late, which is worth knowing when your customer's timeline seems more urgent than you expected.

The Timing That Actually Matters to You

Here is the detail most suppliers miss.

Scope 3 reporting begins in 2027 — but on fiscal year 2026 data.

Fiscal 2026 is happening now. The emissions your operation is generating this year, and the materials you are buying this year, are what your customers will be reporting. They cannot go back and collect that retroactively with any credibility.

That is why supplier data requests have accelerated through 2026 rather than waiting for 2027. Your customers are collecting the baseline while the year is still in progress.

If a request has already landed on your desk, this is usually why. See what automotive customers may ask you to provide.

What Your Customers Will Ask For

SB 253 does not give your customer authority to compel anything from you — you are not a regulated party. What it does is give them a hard reason to ask, and a deadline of their own.

Expect requests for:

• Your Scope 1 and Scope 2 emissions for a defined reporting year, with the boundary and method stated
• Energy consumption by facility, sometimes instead of calculated emissions, so they can apply their own factors consistently
• Product Carbon Footprints for specific part numbers, usually cradle-to-gate
• Your own Scope 3, particularly purchased goods, since your suppliers feed their number too
• Methodology and evidence — emissions factor sources, allocation approach, underlying activity data
• Data quality labelling — what is measured versus estimated

That last pair matters more under a regulatory driver than it did under a voluntary one. When your customer's disclosure carries a $500,000 penalty exposure and eventual third-party assurance, they have to be able to defend the inputs. A number you cannot explain is a number they may not be able to use.

The Safe Harbor Cuts Both Ways

The good-faith safe harbor for Scope 3 disclosures through 2030 is genuinely helpful, and it is worth understanding what it does and does not mean for you.

It means your customer is not expected to produce a perfect supply chain inventory immediately. Estimates and industry averages are acceptable while the data improves.

It does not mean the requests stop. If anything the opposite: the way a company demonstrates good faith is by showing it made a real effort to obtain supplier-specific data. Documented outreach to suppliers is evidence. So the safe harbor rewards asking, and your customers will keep asking.

What it does give you is room. A first-year answer labelled honestly as an estimate is genuinely useful to your customer. "We don't have that" is not.

SB 253 Versus SB 261

These two California laws are frequently confused, and they are different in ways that matter.

	SB 253	SB 261
Revenue threshold	Over $1 billion	Over $500 million
What it requires	Greenhouse gas emissions disclosure, Scope 1, 2 and 3	Climate-related financial risk report
Reaches your data?	Yes, through Scope 3	Indirectly at most
Assurance	Expected from 2027	None
Maximum penalty	$500,000 per year	$50,000 per year
Enforcement status	Proceeding	Enjoined by the Ninth Circuit in November 2025

For a supplier, SB 253 is the one that generates data requests, because it is the one that requires emissions accounting across the value chain. Our guide to SB 261 covers the climate risk side in detail.

What to Have Ready

None of this requires a sustainability department. It requires a small set of things to exist before someone asks for them.

• A Scope 1 and Scope 2 inventory for your most recent full year. This comes almost entirely from utility bills, fuel purchase records, and maintenance logs. For a single-site supplier it is weeks of work, and it is the foundation of nearly every answer.
• A stated boundary and method. Which sites, which period, which emissions factors, location-based or market-based Scope 2. A number without this cannot be used by the recipient.
• A first-pass Scope 3 estimate from purchasing data, clearly labelled as spend-based.
• One documented Product Carbon Footprint for a representative part. The first is the expensive one; the method carries over.
• Data quality labelling — measured, supplier-provided, calculated, estimated.
• An evidence pack — environmental policy, certifications, methodology note, source data — kept current rather than assembled per request.

Suppliers with this in place answer in days. Suppliers without it spend several weeks per request, every time.

One Dataset, Several Destinations

It is worth noting that SB 253 is not a separate workstream from everything else your customers are asking about.

The same underlying data — facility energy, emissions by scope, part-level footprints, methodology, evidence — feeds:

• SB 253 Scope 3 requests from U.S. customers
• EU CSRD reporting for customers with European operations
• Catena-X Product Carbon Footprint exchange
• The Drive Sustainability SAQ and EcoVadis assessments
• Customer-specific questionnaires and scorecards

Suppliers who build this once and maintain it handle each new requirement as a reformatting job. Suppliers who treat each request as a separate project rebuild the same numbers several times a year, indefinitely.

That is the practical argument for treating this as infrastructure rather than compliance response. See automotive Scope 3 emissions for how the pieces connect.

A Note on the Litigation

It is tempting to wait and see whether the courts strike the law down. That is a reasonable thing to watch and a poor thing to plan around, for three reasons.

First, the Ninth Circuit declined to enjoin SB 253 even while pausing SB 261, which is a meaningful signal about how the two are being treated.

Second, your customers are not waiting. Their planning assumption is compliance, and their supplier data programs are running now regardless of how the appeal resolves.

Third, and most importantly, almost nothing you would do to prepare for SB 253 is wasted if it disappears tomorrow. A Scope 1 and 2 inventory, a repeatable product footprint method, and a documented evidence pack are what EU customers, Catena-X, EcoVadis, and the SAQ all require anyway. California is a deadline, not a reason.

How Aclymate Helps

Aclymate works both sides of this: companies that need to collect supplier data for their own disclosure, and suppliers that need to produce it.

• Navigator — Scope 1, 2 and 3 carbon accounting that retains its inputs, so methodology questions are answerable later
• Product Footprint Pack — repeatable part-level footprints from bills of materials
• Supplier & Scope 3 Data Support — collecting from your suppliers and packaging what goes to your customers
• Supply chain sustainability consultants — for working out what a specific customer request actually requires
• Reporting support — customer responses, questionnaires and sustainability reports

Software plus expert services, which suits a supply base where most companies will never employ a sustainability specialist.

See the Automotive & Transportation page, or OEM sustainability requirements for the full picture of what customers ask for.

Regulatory details in this article were verified in September 2026. SB 253 rulemaking is ongoing and the Ninth Circuit appeal is undecided, so confirm current requirements with CARB or your customer's compliance team before acting on a specific date.