The Telephone Consumer Protection Act (TCPA) governs automated calls and texts to US phone numbers, and it sets a meaningfully higher bar than CAN-SPAM does for email: for marketing text messages sent via automated systems, prior express written consent is generally required before the first message goes out, not merely an opt-out option after the fact. The practical reason SMS compliance gets treated more cautiously than email across the industry is litigation exposure — TCPA carries statutory damages per violation that can be claimed without having to prove actual financial harm, and it has historically drawn significant class-action activity, which makes a sloppy SMS consent process a direct legal liability in a way sloppy email practices usually aren't. Treat the specifics below as a conceptual map; the exact consent language and documentation requirements are the kind of detail to confirm with counsel before launching an SMS program.

Email (CAN-SPAM) vs. SMS (TCPA) compliance posture

Dimension	Email / CAN-SPAM	SMS / TCPA
Consent model	Opt-out — can send until recipient objects	Opt-in — prior express written consent generally required
Damages exposure	FTC/regulatory enforcement, no easy private right of action	Statutory per-message damages, common class-action target
Documentation bar	Suppression list, unsubscribe honored	Documented consent record, ideally with timestamp/method
Timing restrictions	No federal quiet-hours rule	Quiet hours generally apply (commonly framed around 8am-9pm recipient local time)
Opt-out word	Unsubscribe link	Reply STOP must be honored immediately

What counts as valid consent for SMS

Consent for marketing text messages generally needs to be specific to SMS — a customer who gave their phone number at checkout for order-status purposes has not thereby consented to receive promotional texts, and a single blanket checkbox covering email, SMS, and phone calls together is a common, risky shortcut. A defensible consent flow typically separates the SMS opt-in from other consent, discloses that message frequency and data/message rates may apply, states the purpose (marketing vs. transactional/order updates), and is recorded with enough detail (timestamp, method, exact language shown) to reconstruct later if challenged. Consent obtained for one purpose generally should not be assumed to cover an unrelated purpose.

sms_consent_checklist.txt

text

[ ] SMS opt-in is a distinct checkbox/action, not bundled
    with email opt-in or required to complete checkout
[ ] Opt-in language discloses: message frequency may vary,
    message/data rates may apply, purpose of messages
[ ] Consent event logged: timestamp, exact disclosure text
    shown, method (web form, keyword text-in, POS, etc.)
[ ] Welcome/confirmation message sent on opt-in, restating
    how to opt out (reply STOP) and get help (reply HELP)
[ ] STOP keyword wired to immediately suppress future sends
    across ALL sending tools/platforms, not just one
[ ] Send times restricted to compliant local-time window
[ ] Consent records retained — not just the current state but
    a historical log, in case of a later dispute

Reply STOP has to work everywhere, immediately

If a customer texts STOP and still receives a promotional message days later because the suppression didn't propagate to every sending platform or queued campaign in time, that's a direct compliance failure with real litigation exposure — not a minor delivery glitch. Any brand running SMS through multiple tools (an ESP/SMS platform plus a separate transactional provider, for instance) needs a single source of truth for opt-out status that every sending system checks before every send, not a per-platform suppression list that can drift out of sync.

Quiet hours and frequency

TCPA-related guidance and industry carrier rules generally expect marketing texts to be sent only during a reasonable daytime window in the recipient's local time zone, which means a national SMS send needs to account for time zone at the recipient level, not fire a single blast at a single clock time regardless of where the recipient lives. Message frequency also matters beyond strict legal compliance — carriers and mobile network operators apply their own filtering against senders with high complaint rates or aggressive frequency, which can get a sending number or short code throttled or blocked independent of any legal violation.

Risk factors that compound TCPA exposure

Risk factor	Why it matters
Purchased or scraped phone lists	No valid consent exists at all — high-risk by default
Bundled consent checkboxes	Hard to prove SMS-specific consent if challenged
No consent record retention	Can't defend consent validity in a dispute
Cross-platform STOP not honored	Direct, provable violation per message sent after opt-out
Autodialed/automated systems	Triggers the stricter prior-express-consent standard

SMS's higher bar is also its advantage

Precisely because SMS requires a cleaner, more deliberate opt-in than email, SMS lists tend to have higher engagement rates once built — recipients who went through a genuine opt-in understand what they signed up for, which is reflected in generally higher open and click-through rates compared to email. The stricter compliance requirement and the channel's effectiveness are related, not opposed: the friction that keeps the list smaller also keeps it higher-intent.

What's next

Consent requirements for SMS are one piece of the broader consent-capture problem that cookie banners and CMPs exist to solve on the web side. Next: Cookie Consent Banner UX →

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