It's a security issue. They'll want biometric checks, depth of anal cavity etc. Seriously it is unusual for FAA to be so awkward
I believe you only need this by I think 5th March to get the English language endorsment if you wish to fly N reg out of the USA. eg. Canada, Bahamas or Mexico.
I think you can still fly "N" in the UK on your CAA/JAA licence.
DO.