In my Google Developer Console, there are warnings for several apps as
We have determined that your app uses a library or SDK (com.google, com.google.ads) that is in violation of the Developer Program Policy. Please note that beginning Aug 1st, 2014 the Developer Program Policy requires all updates and new apps uploaded to be compliant with the advertising ID provision of the Developer Program Policy. Apps in violation may be subject to permanent removal from the Store.
I am using google play services library only in those apps for advertising. What would be the reason for that?