If you go to the first blank line, than select to the bottom of the spreadsheet (or way down at least), and then remove the selection (right click, remove - if that's the correct English term), which is not the same as deleting the contents, it might work. Otherwise, you would have to do something (add some selection) to the process/program making the labels. If you explain how you do that (it's NOT File>Generate>Labels or something like that, I suppose) some help might come.

Kees