Yes, you need a permit. Don't pretend you don't know, because they don't care. Its a nasty fine, and they are taking this extreme measures because this is a serious problem. Canas are to the point in many states, where we may loose all aquatic plant life and a lot of aquatic animal life from ammonia/NitrIte/NitrAte issues from overpopulation of canas. Since canas and brigs are so closely related, permits are required to accompany all boxes. They will distory stock and hunt you down if they find a box without a permit.
The permits are free, but do take some time and effort to aquire. Expect at least a week turn around (up to 6 but none of mine ever took more than 14 days) to recieve electronic permits, you print copies as needed. You will need one for each state, excluding Hawaii and the state you live in. FL and gulf states as well as CA may also be denied because of local laws, but mine were all approved last summer.
Go here http://www.aphis.usda.gov/plant_health/permits/
Select I want to.... register for permits on the right of the screen. You will need to be 18 (or have a parent register.) This will give you level 1 access to the site. To get a permit/s, you need level 2 access. To get level 2 access you must go to a local USDA office in person with a state ID. There an agent will take your id, copy it, and clear you for level 2 access. Within 48 hours from being cleared, you must register a new secure password with the site. All these directions will be emailed to you when you request level 2 access after registering level 1 on the site.
Following this you must complete the permit application. A tip, use the "copy" feature and then just change the state. I heard they are working on a "all states" version, but I haven't heard word. Another tip, place "commercial resale no breeding involved", then you only need the state in the recieving address, instead of a full address.