If the bachelors and masters degree are closely related to each other and to the
TN category for which you are applying, then taking both degreess as they are should be suffcient.
Otherwise, especially if you are either using an unrelated degree or your bachelor degree is the only related degree, then you need an eval.
Ex: If you have both a Bach and ME in Engineering and are applying for a software engineering postion, you're fine. If you have Bach Eng and and MBA and are applying for engineering job, get an eval.
If you bachelors is non-English, you should get an eval in any event for future use.