SAE is a standard used to measure towing capacity for trucks (and cars) with a payload of less than 14,000 payload (up from 13,000), not a rule or law but a voluntary standard. It just puts everyone on an equal footing so the consumer can compare towing capacities among vehicles and not have one manufacturer exaggerate their claims.
Ford finally agreed that it would use the J2807 on new or redesigned trucks so the F-150 for 2015 is certified for J2807 but not previous models. Toyotas are certified starting in 2013. Ram and GM 1500-series pickup trucks were certified to SAE J2807 as soon as it was clear that Ford was going to follow through. Nissan is the only holdout at this time.
Standardized Tow Rating Procedure Finally Gaining Traction | Edmunds.com
All the unrealistic test weight practices of the past that led to asterisks and fine print have been eliminated. Maximum tow ratings can no longer be based on a stripped base-model truck with a 150-pound driver traveling alone. Test trucks must now be equipped with popular options found on 33 percent (or more) of the configuration being tested. The 150-pound test driver is now accompanied by a 150-pound passenger.
Cars.com has an article on this as well.