I'm having trouble finding a source outside of an oblique reference in the Wikipedia article for NSLs, but yes, you can talk to an attorney about the letter. Th

I'm having trouble finding a source outside of an oblique reference in the Wikipedia article for NSLs, but yes, you can talk to an attorney about the letter. This was not the case originally (or at least in the opinion of the government), but the law was changed to allow consulting with a lawyer (and challenging the letter in court as well). IANAL, but I play one on the Internet.