Unless you know for a fact that the employer in question allows the type of facial hair that you have, you should shave it off. Since you don't actually work there yet, you could probably get away with it but why take a chance.

It is a known fact that people tend to consider someone with facial hair to be less trustworthy than cleanshaven men. This is a subconscious perception thing, there's no good reason for it, but it is what it is.

Very few airlines allow anything but a short mustache. JetBlue is the notable exception, they have allowed goatees but I heard that's going away. Some small commuter outfits might also be lenient.