If you're on a work visa you're obviously allowed to work. If you enter on a tourist visa (or visa waiver, whose conditions are usually the same as tourist vis

If you're on a work visa you're obviously allowed to work. If you enter on a tourist visa (or visa waiver, whose conditions are usually the same as tourist visa) they want to be sure you aren't committing visa fraud and planning to work. That's what causes the grilling.