According to a report yesterday by Bloomberg, some Android apps may be using silent push notifications to track if and when you uninstall them, which is alleged to be a violation of both Apple and Google's policies. Ostensibly this is being done to target such users with advertisements designed to win the back, although the tracking providers claim this functionality is designed to gauge response to app updates and changes.
We haven't been able to find the precise section of Google's developer terms which this behavior is alleged to be a violation of, though there are a few broader API terms it could be shoehorned to fit into violating. However, Bloomberg received a comment from Alex Austin, CEO of Branch Metrics Inc., who claims that it is a violation, and regardless of Google's terms he thinks (and we agree) that, "it’s just generally sketchy to track people around the internet after they’ve opted out of using your product."
Bloomberg lists a series of companies which design solutions that include this silent push notification tracking behavior, and note that customers for these companies include T-Mobile, Spotify, Yelp, and Bloomberg's own parent company.
At a technical level, the tracking operates by pinging apps via push notifications silently at regular intervals and making a note when each device no longer responds to such queries. By including and recording a unique advertising ID with that data, it would be hypothetically able to track and target that device with future advertisements.
Details at this point are sparse, with no apps verified as using this tracking behavior (yet). Google did not respond to Bloomberg for comment, so we'll have to wait and see if anything comes from this revelation. In the meantime, feel free to click through to Bloomberg's coverage for more information on the subject.