AWA explains Google's policy towards pop-ups.
[Link to quote
Quoting from the 'Links' section of the AdWords Editorial Guidelines, here is the pop-up policy:
We do not allow links to landing pages that generate pop-ups when users enter or leave your landing page. We consider a pop-up to be any window, regardless of content, that opens in addition to the original window.
BTW, many advertiser are not aware that there is a link to the Editorial Guidelines at the bottom of every page in their account. These are worth reviewing from time to time IMO, as they do evolve.