Your tenth employee switches on Proposition 65, and it is one afternoon of work

A certified letter turns up. It is a 60 day notice, it is not from any agency you have heard of, and it says your business exposed people to a listed chemical on a job you finished months ago without giving them a warning. Nobody was hurt. Nobody complained. The letter is about a sign that was not there.

Proposition 65 has a reputation among contractors as either a joke about coffee shops or a lawsuit machine that comes out of nowhere. It is neither. It is a narrow duty that switches on at a specific headcount, applies in a specific way to construction work, and is satisfied by wording somebody else already wrote for you. The entire thing is a setup job: an afternoon once, a diary note once a year, and two signs behind the seat of the truck.

Here is the whole of it, with the section behind each number.

It starts at ten employees, and it counts your business

The warning duty falls on a person in the course of doing business, and that phrase specifically excludes any business employing fewer than 10 employees (Health and Safety Code s.25249.11(b)).

That is a real line, not a technicality. A four person framing outfit does not carry this obligation. The day you put on your tenth person, you do, and the switch flips on the payroll rather than on the job. It counts your business, not the crew standing on any one site, so a company with eleven people spread across three jobs is inside it and a general contractor coordinating forty people from six different subs is counted on their own eleven.

Two things follow from that. If you are growing, this belongs on the same checklist as the workers compensation, payroll and safety items that arrive with a headcount, which is the first employee sequence extended a few hires further. And if you are under ten, read the rest of this page anyway, because the general contractor above you will often push the warning obligation down to you by contract whether or not the statute reaches you.

The duty is a warning, given first

Section 25249.6 says a business shall not knowingly and intentionally expose anyone to a listed chemical without first giving a clear and reasonable warning.

The load-bearing word is "first". The warning goes up before the exposure happens, which on a construction site means before the saw starts, not in the closeout package and not on the invoice. A warning that arrives after the dust does is not a late warning, it is no warning.

"Clear and reasonable" is the other half, and this is where California does you a favor: the state publishes safe harbor content and methods in the warning regulations at 27 CCR 25600 and following. A warning that follows the regulation is deemed clear and reasonable. One you wrote yourself might be, and you would be arguing about it from behind.

Three places a contractor actually meets it

Your own crew. Exposures to your employees are occupational exposures, and they are handled through the hazard communication program you already owe under Cal/OSHA: the labels, the safety data sheets and the training (8 CCR 5194). If your HazCom program is real, this side is largely already done, and it sits naturally with the written safety program in the IIPP guide.

Everybody else at or near the work. This is the environmental exposure and it is the one that generates letters. The office suite next to the tenant improvement. The residents of the other units in the building. The tenants in the occupied half of a retail center while you cut and core the other half. The public walking past an open sidewalk shed. These people are not in your HazCom program and never will be, so the warning has to reach them another way, which in practice is a posted sign where they will actually see it before they walk into the area.

Property and products. If you own, lease or manage the building, or you sell or install a product that carries its own warning, the obligation travels with that too. Check what the manufacturer already put on the label before you write anything yourself.

What the sign says

The safe harbor warning content comes from the regulation rather than from your imagination (27 CCR 25600 and following). The recognizable elements are the black exclamation point inside a yellow triangle, the word WARNING in capitals, a statement that the area or product can expose you to a chemical known to the State of California to cause cancer or reproductive harm, at least one chemical named for each hazard being warned about, and the state's Proposition 65 website address.

Name the chemical. That is the part homemade signs get wrong. A generic warning that names nothing is the version that gets argued about.

The listed chemicals a construction business is most likely to actually encounter are the obvious ones: respirable crystalline silica from cutting, coring, grinding and dry sweeping concrete and masonry, lead from older paint and from some solders and flashings, wood dust from milling and sanding, asbestos in pre 1980s building materials, diesel engine exhaust around equipment, and carbon monoxide from anything burning fuel in an enclosed space. The list itself is published by the state and it changes, which is why the annual review below exists. If your work involves disturbing lead paint or asbestos containing material, the licensing and registration side of that sits in the asbestos abatement guide.

The twelve months after a listing are yours

A chemical newly added to the list carries no warning obligation for the first twelve months after it goes on (Health and Safety Code s.25249.10(b)).

That single provision is what makes this a once a year job rather than a running worry. You cannot be caught out overnight by a listing you did not notice this morning. Put a recurring note in your calendar for the same week every January, spend fifteen minutes checking the current list against the materials you actually handle, and you have a full year of cover on anything added since.

The arithmetic behind the letter

Enforcement runs two ways. Public prosecutors can act, and so can private enforcers, and the private route is the one contractors meet. A private enforcer has to serve a 60 day notice on the business and on the public prosecutors first, and can only bring the action after those 60 days if no public prosecutor has taken it up (Health and Safety Code s.25249.7(d)).

Put a date on it. A notice served Tuesday 14 July 2026 means the earliest a private action can be filed is Saturday 12 September 2026. That is your window, and it is the whole reason the notice exists: two months to establish whether the exposure happened, whether you were even a person in the course of doing business at the time, whether a warning was actually given, and what the site looked like on the days in question.

The penalty is up to $2,500 per day per violation (Health and Safety Code s.25249.7(b)), which is arithmetic run on the number of days rather than on the harm. A 90 day job with no sign on it is 90 times $2,500, which is $225,000 as a statutory ceiling before anyone argues about anything. That number is why these get settled rather than tried, and it is also why a photograph of your posted sign, dated, in the job file, is worth more than any argument you can make later.

Take one photo of the sign in place on the first morning of every job that needs one. It costs ten seconds and it is the entire defense.

The other half nobody reads: what you pour on the ground

Section 25249.5 is the discharge side. A business shall not knowingly discharge a listed chemical into water, or onto land where it passes or probably will pass into a source of drinking water.

For a contractor that is concrete washout, saw cutting slurry, dewatering, and whatever comes off a pressure wash and finds a storm drain. It runs alongside the stormwater rules rather than replacing them, and the controls are the same controls: containment, a washout area, and not letting the slurry reach the drain. Coverage kicks in at one acre of disturbance for the stormwater permit itself, and the practical build of that is in stormwater and SWPPP for California contractors.

The afternoon, in five steps

1. List what you actually handle. Pull the safety data sheets you already keep and write down the materials and processes on your real jobs. Silica, lead, wood dust, exhaust, solvents and sealers cover most residential and light commercial work.
2. Decide which sites put non-employees in reach. Occupied buildings, shared parking, public sidewalks, multi tenant work. On a bare lot with a fence around it and nobody but your crew inside, the environmental exposure question mostly answers itself.
3. Buy the signs. Regulation format, at least one chemical named for each hazard, laminated, two spare in the truck.
4. Put a clause in your paperwork. Who posts the warning, where, and from when. In your subcontract for the work you buy, and in your customer contract for the work you sell. If you do residential remodeling, it goes into the same contract pack as the rest of the required language in the home improvement contract guide.
5. Diary the January review. Fifteen minutes against the current list.

That is it. Five steps, one afternoon, and then it is a thing your business does rather than a thing you think about.

Do it before the tenth hire, not after the letter

Proposition 65 punishes businesses that were not set up, not businesses that made mistakes. There is no inspection, no filing, no registration and no fee anywhere in it. The obligation is a sign, the wording is published, the headcount trigger is a number you already know, and the annual review takes a quarter of an hour. Every part of it is knowable and fixed in advance, which means the contractor who spent one afternoon on it is simply not in the population these letters get sent to.

On AEC Stack there is no monthly subscription. The platform fee is 2.5 percent of each invoice processed through the platform, so the job file that holds your site photos, your subcontract terms and your dates is paid for by the jobs that actually get paid.

Count your employees. If the answer is nine or more, order the signs this week and take the photo on your next job. Then open a working business file and keep the dated site photo with the job it belongs to, where you can find it two years later.