Although in Puerto Rico we are governed by most of US laws. I have imported fertilizer in small and medium quantities an some of the packages have been inspected. When I had more plants I used to buy fertilizer in 50 lbs bags. I had a couple of visits from the FBI, DEA and ATF, very educated persons mind you. WHY? Fertilizer can be used to make explosives! Don't know if you are old enough to remember the Oklahoma blasting where a whole building was destroyed and many lives lost, including children. The explosive device was a truck filled with Nitrogen based fertilizer and an accelerant. So maybe that is the problem. Maybe you can contact the authorities and arrange for a visual inspection of your growing area. That usually takes care of it.