More than one source of income while on a TN?

No one seems to know the precise answer to this: I am a TN holder with a regular W2 paycheck from my employer. My tax preparer says I can receive (passive) royalties from a book I wrote while on TN (it's being released in a few weeks) and also passive income on my blog from google ad sense, but I CAN NOT start a writing service or record teaching CDs and charge customers on the side. This latter would be a case of more than one employer -- a TN no-no. Is this correct? If, then I don't understand the distinction between passive and "active" income.
Thanks!
Padraig

You can have many employers on TN, but thet EACH need to sponsor you.

Your new activities would not be passive, and would not have an employer/sponsor, so would violate TN status.