Thanks for the warning. Are you talking about entering and first applying for the TN-1 or anytime during the visa's length (e.g. visit's back home for Christmas)?
In my case, i was asked by my employer to remain in the US for the length of the visa, as me being potentially unable to get back to the office was considered to be a business risk. Needless to say, that was rather displeasing, and eventually led to my departure from the company.