Fuel carry question

[AbleGuy]

I've noticed in some videos I've seen lately where someone with long range fuel tanks and rotopax would talk about having 60 or 70 gallons of fuel onboard. I seem to recall hearing some time ago that if you have more than 50 gallons of fuel that you need a special permit. Is that true, and if so, what is involved in getting that permit. I'm starting to thinking about getting long range tanks is why I ask.