They may be unconstitutional (fed district court in SF so ruled in March 2013, appeal pending), so the question of whether it is lawful seems to be open. Edit:

They may be unconstitutional (fed district court in SF so ruled in March 2013, appeal pending), so the question of whether it is lawful seems to be open. Edit: I see that you are asking about telling counsel about the NSL. The text of the NSL explicitly states that you may seek legal counsel.