Competitor False Advertising in California: Legal Options and the Letter

Can you stop a competitor's false advertising in California?

Yes, if the claim is false or misleading and it is costing you business. California's false advertising law makes it unlawful to make or spread any statement, including over the internet, that is untrue or misleading and that the advertiser knew, or by reasonable care should have known, was untrue or misleading (Business and Professions Code section 17500).

The Unfair Competition Law, or UCL, covers any unlawful, unfair or fraudulent business practice and any untrue or misleading advertising, including anything that violates section 17500 (section 17200). Federal law adds a third route: Lanham Act section 43(a) lets any person who believes they are or are likely to be damaged sue over commercial advertising that misrepresents the nature, characteristics, qualities or geographic origin of goods or services (15 U.S.C. section 1125(a)(1)(B)). Courts apply further limits on which plaintiffs qualify, so ask a lawyer whether you do.

A cease and desist letter is a low-cost opening move. It names the claim, shows why it is false and asks for it to come down. If you are unsure how that kind of letter differs from a demand for money, see our guide to what a cease and desist letter means.

California false advertising law, the UCL and the Lanham Act compared

Restitution under the state laws means returning money or property acquired through the unlawful practice, which is not the same as recovering your lost profits. That difference is one reason to ask a lawyer whether the federal claim also fits.

What can a competitor lawfully say about your product?

Truthful comparison is generally allowed. A competitor can name your brand and compare price, features or test results, as long as the comparison is accurate and not misleading. What crosses the line is a specific, checkable claim that is false or that leaves a misleading impression.

For businesses advertising to California consumers, section 17508(a) singles out three claim types: claims that purport to rest on factual, objective or clinical evidence; claims comparing a product's effectiveness or safety to other brands; and claims purporting to be based on any fact. False or misleading claims of those kinds are unlawful. The Attorney General, district attorneys, city attorneys, county counsel and the Director of Consumer Affairs may also demand the evidence behind such a claim, within one year of the last day it ran (section 17508(b)).

• Likely opinion or puffery: "the friendliest service in town," "our favorite blend."
• Measurable and testable: "twice as fast as Brand X," "lab-tested to remove 99.9 percent of allergens," "the only state-certified installer."
• Misleading by omission: a price comparison that leaves out a mandatory fee, or test results from a product version no longer sold.

If the problem is a rival using your brand name or logo in a way that confuses buyers, that is a trademark issue; see our trademark cease and desist letter guide.

Example: one ad, three problems

Example (hypothetical): a water filter company sees a competitor's paid search ad and landing page with these lines.

The third line is about you rather than their product, so it may also raise trade libel questions. A letter would address each line separately and ask for each one to be removed.

Building the letter: evidence first, then the demand

Your letter is only as strong as the proof that the statement is false and that it reached buyers. Collect it before you write, and keep originals in case the ads change.

1. Capture every version of the claim: web pages, paid ads, social posts, packaging and sales sheets, with dates and URLs.
2. Assemble proof of falsity, such as test data, certifications, published specs or public records.
3. Document harm: lost bids, customers who cited the claim, a drop in sales after the campaign began.
4. Check your own advertising for claims the competitor could challenge in return.
5. Identify the right recipient, ideally the company's legal department or registered agent; the steps for finding a business's legal name apply here.
6. Write the demand: quote each claim, explain why it is false, and ask that it be removed or corrected by a set date.
7. Ask the competitor to preserve its ad files and substantiation, and keep yours.

What happens if the competitor ignores the letter?

You have several paths, and they can be combined:

• Lawsuit for an injunction under the UCL or section 17500 in state court, or under the Lanham Act in federal court. UCL claims must be brought within four years of accrual (section 17208).
• Report to public enforcers. The Attorney General or a local district attorney can investigate, request substantiation under section 17508 and seek civil penalties.
• Platform complaints. Ad networks and marketplaces have their own policies on misleading claims and may remove ads that break them.

The competitor may answer through counsel, and may question your own advertising in return. Our guide to receiving a cease and desist letter shows what the other side will be weighing.

Sending a false advertising demand through an attorney

A false advertising demand may end up on the competitor's lawyer's desk, and it can invite a close look at your own ads. Attorney drafting is worth weighing when the claim targets your brand by name, when a campaign is running across several channels, when you may need an injunction, or when you want the letter to set up claims under both California law and the Lanham Act.

Through Talk to My Lawyer, a licensed California attorney writes your letter from your screenshots, test data and sales records, ties each challenged claim to the law it violates, and sends it on your behalf. Whether to file suit, and in which court, is a question for a lawyer who has seen your evidence.