Printing on pre-printed labels

[admiralsboy]

Hello. I hope I can get assistance with an head scratcher. At my work, we have to add a code to pre-printed labels that we receive. I have no clue where these labels originate. They are four inches wide by two inches tall and come fan folded, not on a roll.

I have tried an inexpensive thermal label printer but apparently these labels are not made of thermal reactive paper. I am looking for an inexpensive printer able to print on these labels in as direct a path as possible from a fan fold source.

Any advice or guidance in my research would be appreciated. Thank you in advance.