Mayors Against Illegal Guns started its FixGunChecks.org Truck Tour on Wednesday.
The truck will travel the country for two months to publicize what the group says are flaws in the nation's gun background check system.
The truck features a clock that will toll the number of Americans killed with guns since the Jan. 8 shootings in Tucson, Ariz. that killed six people.
The mayors want Congress to pass a law that would subject every gun sale to a background check.
They also want the names of people prohibited from buying a gun in a central database.